docs: issues on the GitHub mirror, with bug and feature forms

The README says pull requests aren't taken and points to issues on the
GitHub mirror. Issue forms for bug reports and feature requests set the
bug and enhancement labels; blank issues are off.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -100,6 +100,14 @@ call of its own is a daily check for a new release on this server, which
 `updateCheck: false` turns off.
 
 
+## Contributing
+
+I don't take pull requests: I don't have time to review and test them.
+Bug reports and ideas are welcome, though: open an
+[issue on GitHub](https://github.com/karleinarb/lazysecrets/issues), as a
+bug report or a feature request, and I'll have a look.
+
+
 ## AI disclosure
 
 Built with help from an agentic coding assistant. Every change is requested, reviewed and tested by me before it's merged.