Document manual installation steps

src/content/docs/docs/gettingstarted.mdx

@@ -16,8 +16,29 @@ Skip requires a macOS 15+ development host with [Xcode 16](https://developer.app
     brew install skiptools/skip/skip
     ```
 
-    This will download and install the `skip` tool itself, along with the Android SDK and `gradle` build tool that is necessary for building and running the Android side of your apps.
-
+    This will download and install the `skip` tool itself, along with `swiftly`, the Android SDK, and the `gradle` build tool that is necessary for building and running the Android side of your apps.
+
+1. If you've never used `swiftly` before, you'll need to initialize it with `swiftly init`.
+
+1. You'll need to ensure that `xcodebuild -version` is working. When you try it, you may see this error:
+
+    ```console
+    xcodebuild -version
+    ```
+
+    ```plaintext
+    xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer
+    directory '/Library/Developer/CommandLineTools' is a command line tools instance
+    ```
+
+    To resolve this error, run this:
+
+    ```console
+	sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
+    ```
+
+    You'll need to enter your macOS password to update it. (If you prefer, you can open Xcode, navigate to Settings --> Locations, and update "Command Line Tools", changing it to your current version of Xcode.)
+
 1. You can ensure that the basic development prerequisites are satisfied by running:
 
     ```console
@@ -50,7 +71,7 @@ Skip requires a macOS 15+ development host with [Xcode 16](https://developer.app
     [✓] Skip checkup succeeded in 190.21s
     ```
 
-    If the installation or checkup fails, try running again with `skip checkup --verbose` to get more details, and check the [FAQ](/docs/faq/) for common solutions or reach out to the community on [Slack](/slack/) or the [Discussion Forums](https://forums.skip.dev).
+    If the installation or checkup fails, try running again with `skip checkup --verbose` to get more details, and check the [Getting Help](/docs/help/) for common solutions or reach out to the community on [Slack](/slack/) or the [Discussion Forums](https://forums.skip.dev).
 
 1. Create a new Skip app project with:
 

src/content/docs/docs/help.md

@@ -13,3 +13,58 @@ Skip's architecture relies on recent advances in the plugin system used by Xcode
 
 Specific known error conditions are listed below. Search the [documentation](/docs), [issues](https://source.skip.dev/skip/issues), and [discussions](http://forums.skip.dev) for more information and to report problems.
 
+### `skip doctor` / `skip checkup` errors
+
+#### "Swiftly version: error executing swiftly"
+
+[`swiftly`](https://github.com/swiftlang/swiftly) is a tool to install and manage Swift toolchains. Homebrew installs `swiftly` when you install `skip`.
+
+If you've never used `swiftly` before, you'll need to initialize it, by running `swiftly init`. Then, `swiftly --version` should run and provide you with a version number. Once `swiftly --version` works, `skip doctor` will no longer have an error executing `swiftly`.
+
+#### "Xcode version: error executing xcodebuild"
+
+When you view the log, you'll probably see an error like this:
+
+```plaintext
+xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer
+directory '/Library/Developer/CommandLineTools' is a command line tools instance
+```
+
+To resolve this error, run this:
+
+```console
+sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
+```
+
+You'll need to enter your macOS password to update it. (If you prefer, you can open Xcode, navigate to Settings --> Locations, and update "Command Line Tools", changing it to your current version of Xcode.)
+
+#### "xcodebuild: error: Unable to find a destination matching the provided destination specifier:"
+
+Check the `skip checkup` log, and you might find an error like this:
+
+```plaintext
+xcodebuild: error: Unable to find a destination matching the provided destination specifier:
+    { generic:1, platform:iOS }
+Available destinations for the "HelloSkip App" scheme:
+    { platform:macOS, arch:arm64, id:01f95e76beb7a42fa85328bb400a00e1ed54f993, name:My Mac }
+    { platform:macOS, arch:x86_64, id:01f95e76beb7a42fa85328bb400a00e1ed54f993, name:My Mac }
+    { platform:macOS, name:Any Mac }
+Ineligible destinations for the "HelloSkip App" scheme:
+    { platform:iOS, id:dvtdevice-DVTiPhonePlaceholder-iphoneos:placeholder, name:Any iOS Device, error:iOS 26.2 is not installed. Please download and install the platform from Xcode > Settings > Components. }
+```
+
+In this case, you'll need to install the iOS SDK in Xcode > Settings > Components.
+
+#### "SDK location not found. Define a valid SDK location with an ANDROID_HOME environment variable"
+
+You'll typically see this error in the log when the "Test Kotlin" step fails during `skip checkup`. The full error typically looks like this:
+
+```plaintext
+execGradle: /opt/homebrew/bin/gradle testDebug --project-dir /private/var/folders/1l/jbmc3w7947x9ljkj_260bmrc0000gn/T/902632B6-1BB4-47D5-98A1-5E55CF286A78/.build/checkouts/skip/Skip/build/902632b6-1bb4-47d5-98a1-5e55cf286a78/HelloSkipTests/destination/skipstone --warning-mode all -PbuildDir=.build/HelloSkip --rerun-tasks --console=plain
+FAILURE: Build failed with an exception.
+* What went wrong:
+Could not determine the dependencies of task ':HelloSkip:testDebugUnitTest'.
+> SDK location not found. Define a valid SDK location with an ANDROID_HOME environment variable or by setting the sdk.dir path in your project's local properties file at '/private/var/folders/1l/jbmc3w7947x9ljkj_260bmrc0000gn/T/902632B6-1BB4-47D5-98A1-5E55CF286A78/.build/plugins/outputs/902632b6-1bb4-47d5-98a1-5e55cf286a78/HelloSkipTests/destination/skipstone/local.properties'.
+```
+
+You'll need to install Android Studio and run it, which will download the Android SDK and install it in `~/Library/Android/sdk`. (If your Android SDK is installed in another directory, specify it with the `$ANDROID_HOME` environment variable.)