troubleshooting: mention specific HCS_E_HYPERV_NOT_INSTALLED error code

Inspired by docker/for-win#14743

The troubleshooting contains the relevant info, but this PR

- explicitly mentions a common error code (hopefully helping people
  find this advice)
- emphasises that, in WSL 2 mode, WSL 2 commands must be working
  before Docker Desktop can start
- highlight a common scenario where an android emulator is installed
  which disables Hyper-V (because it uses a conflicting hypervisor)

The structure is currently

- WSL 2 only
- Hyper-V only
- Common to both

So add links to the WSL 2 section to the common section to make
sure people realise it's relevant.

Signed-off-by: David Scott <dave.scott@docker.com>

Author: djs55

content/manuals/desktop/troubleshoot-and-support/troubleshoot/topics.md

@@ -343,13 +343,21 @@ Also, the `\` character has a special meaning in Git Bash.
 
 Portability of the scripts is not affected as Linux treats multiple `/` as a single entry.
 
-### Docker Desktop fails due to Virtualization settings
+### Docker Desktop fails due to Virtualization not working
+
+#### Error message
+
+A typical error message is "Docker Deskop - Unexpected WSL error" mentioning the error code
+`Wsl/Service/RegisterDistro/CreateVm/HCS/HCS_E_HYPERV_NOT_INSTALLED`. Manually executing `wsl` commands
+will also fail with the same error code.
 
 #### Cause
 
 - Virtualization settings are disabled in the BIOS.
 - Windows Hyper-V or WSL 2 components are missing.
 
+Note some third-party software such as Android emulators will disable Hyper-V on install.
+
 #### Solutions
 
 Your machine must have the following features for Docker Desktop to function correctly:
@@ -364,6 +372,21 @@ Your machine must have the following features for Docker Desktop to function cor
 
 ![WSL 2 enabled](../../images/wsl2-enabled.png)
 
+It must be possible to run WSL 2 commands without error, for example
+
+```console
+PS C:\users\> wsl -l -v
+  NAME              STATE           VERSION
+* Ubuntu            Running         2
+  docker-desktop    Stopped         2
+PS C:\users\> wsl -d docker-desktop echo WSL 2 is working
+WSL 2 is working
+```
+
+If the features are enabled but the commands are not working, first check [Virtualization is turned on](#virtualization-must-be-turned-on)
+then [enable the Hypervisor at Windows startup](#hypervisor-enabled-at-windows-startup) if required. If running Docker
+Desktop in a Virtual Machine, ensure [the hypervisor has nested virtualization enabled](#turn-on-nested-virtualization).
+
 ##### Hyper-V
 
 On Windows 10 Pro or Enterprise, you can also use Hyper-V with the following features enabled: