docs: add a note about available regions for the Gemini API (#7)

README.md

@@ -29,6 +29,9 @@ See the [go install](https://go.dev/ref/mod#go-install) instructions for more in
 ### API key
 To use `gemini-cli`, you'll need an API key set in the `GEMINI_API_KEY` environment variable. If you don't already have one, create a key in [Google AI Studio](https://makersuite.google.com/app/apikey).
 
+> [!NOTE]
+> For information on the available regions for the Gemini API and Google AI Studio, see [here](https://ai.google.dev/available_regions#available_regions).
+
 ### System commands
 The system chat message must begin with an exclamation mark and is used for internal operations.
 A short list of supported system commands:
@@ -39,7 +42,7 @@ A short list of supported system commands:
 | !p      | Purge the chat history |
 
 ### CLI help
-```
+```console
 $ ./gemini -h
 Gemini CLI Tool