Add notes for gemini triage in CLI

Author: helin24

tool/triage/GEMINI.md

@@ -0,0 +1,10 @@
+Steps for triage when a user asks for help in the CLI:
+- Find the latest open issues in the flutter/flutter-intellij repo that don't have a priority label.
+- Consider the most recently updated issues first. Start presenting issues one at a time to the user.
+- For each issue, give suggestions such as:
+  - Close the issue if it's not relevant any more (e.g. it's been fixed, the code it's referencing is outdated, etc.)
+  - Suggest how to reproduce if it looks like it may be easy to reproduce locally
+  - Ask for a reproduction with a small project if reproduction may be hard locally
+  - Ask for more information and apply a waiting for response label
+  - Note a code pointer for the issue if it could be a good first issue for an external contributor
+  - Suggest a priority and other labels that may be relevant along with reasoning for the priority