docs: add note about first session project identifier prompt

OPENCODE-MCP.md

@@ -75,6 +75,8 @@ EOF
    - `add_memory`
    - `create_skill`
 
+**First session**: The AI will ask you for your project identifier (recommended: your git remote origin URL like `https://github.com/username/repo`). This ensures your project conventions and memories are consistent across machines. If you don't know your git remote, run `git remote get-url origin` in your project directory. If you need to initialize a git repo or set up AI Skills, search for the "Project Setup Guide" skill.
+
 ## Troubleshooting
 
 ### "Cannot connect to MCP server"