Add some troubleshooting steps to readme

Author: kemayo

README.markdown

@@ -27,6 +27,29 @@ Package Control will automatically keep Git up to date with the latest version.
 
 If you don't want to use Package Control, [check the wiki](https://github.com/kemayo/sublime-text-git/wiki) for other installation methods on various platforms.
 
+## Troubleshooting
+
+This package works by running commands as your system `git`. As such, if you have problems with this package, first make sure that git is installed and configured correctly on your system.
+
+You may want to make sure that the `git` binary this plugin is using is the correct one, if you have multiple ones installed. Most git installation guides will be happy to walk you through configuring your system `$PATH` appropriately.
+
+If necessary, set the `git_command` plugin preference to tell us where to look.
+
+### `fatal: unable to auto-detect email address`
+
+Git isn't configured properly. Tell it who you are, by opening a command prompt and doing this:
+
+    git config --global user.email "you@example.com"
+    git config --global user.name "Your Name"
+
+If you've done this and it's still complaining, you probably have multiple copies of git on your system which have different configuration locations, and the one which runs on your command line isn't the one which the shell `$PATH` exposes to Sublime Text.
+
+### `fatal: could not read Username for 'https://github.com': Device not configured`
+
+Git isn't configured to use a system-level ssh-agent, and so it's asking you for a username and password when you try to push / pull. The plugin doesn't know how to ask you for this information.
+
+[Set up a ssh-agent](https://help.github.com/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent/#adding-your-ssh-key-to-the-ssh-agent) and this will stop happening.
+
 ## Acknowledgements
 
 This package contains: