docs: update WSL instructions for standalone GCM paths

Update the WSL documentation to point to the correct standalone
system-wide GCM install, and also add a section about using the standalone\
user-only installer.

The installation path is under `%LocalAppData%` in this case.

Author: mjcheetham

docs/wsl.md

@@ -44,7 +44,7 @@ _Inside your WSL installation_, run the following command to set GCM as the Git
 credential helper:
 
 ```shell
-git config --global credential.helper /mnt/c/Program\ Files/Git/mingw64/libexec/git-core/git-credential-manager-core.exe
+git config --global credential.helper /mnt/c/Program\ Files\ \(x86\)/Git\ Credential\ Manager/git-credential-manager-core.exe
 
 # For Azure DevOps support only
 git config --global credential.https://dev.azure.com.useHttpPath true
@@ -60,6 +60,13 @@ SETX WSLENV %WSLENV%:GIT_EXEC_PATH/wp
 
 After updating the `WSLENV` environment variable, restart your WSL installation.
 
+### Using the user-only GCM installer?
+
+If you have installed GCM using the user-only installer (i.e, the `gcmuser-*.exe`
+installer and not the system-wide/admin required installer), you need to modify
+the above instructions to point to `/mnt/c/Users/<USERNAME>/AppData/Local/Programs/Git\ Credential\ Manager/git-credential-manager-core.exe`
+instead.
+
 ## How it works
 
 GCM leverages the built-in interoperability between Windows and WSL, provided by