Add links to supported locations and minor fixes (#16476)

docs/troubleshooting.md

@@ -28,6 +28,16 @@ topics on:
     - **Organizational Users:** Contact your Google Cloud administrator to be
       added to your organization's Gemini Code Assist subscription.
 
+- **Error:
+  `Failed to login. Message: Your current account is not eligible... because it is not currently available in your location.`**
+  - **Cause:** Gemini CLI does not currently support your location. For a full
+    list of supported locations, see the following pages:
+    - Gemini Code Assist for individuals:
+      [Available locations](https://developers.google.com/gemini-code-assist/resources/available-locations#americas)
+    - Google AI Pro and Ultra where Gemini Code Assist (and Gemini CLI) is also
+      available:
+      [Available locations](https://developers.google.com/gemini-code-assist/resources/locations-pro-ultra)
+
 - **Error: `Failed to login. Message: Request contains an invalid argument`**
   - **Cause:** Users with Google Workspace accounts or Google Cloud accounts
     associated with their Gmail accounts may not be able to activate the free
@@ -137,7 +147,8 @@ This is especially useful for scripting and automation.
 
 - **Core debugging:**
   - Check the server console output for error messages or stack traces.
-  - Increase log verbosity if configurable.
+  - Increase log verbosity if configurable. For example, set the `DEBUG_MODE`
+    environment variable to `true` or `1`.
   - Use Node.js debugging tools (e.g., `node --inspect`) if you need to step
     through server-side code.