Add .claude directory (stripe#1800)

* add .claude directory

* update instructions

Author: xavdid-stripe

.claude/CLAUDE.md

@@ -0,0 +1,47 @@
+# stripe-ruby
+
+## Testing
+
+- Run all tests: `just test`
+- Tests use Rake (`bundle exec rake test`)
+- Typecheck: `just typecheck` (Sorbet, requires Ruby >= 2.7)
+
+## Formatting & Linting
+
+- Format: `just format` (uses rubocop with auto-correct)
+- Lint check: `just format-check` (rubocop without auto-correct)
+
+## Key Locations
+
+- Main client (HTTP requests, headers, auth): `lib/stripe/stripe_client.rb`
+- Connection management: `lib/stripe/connection_manager.rb`
+- Version: `lib/stripe/version.rb`
+- Sorbet type definitions: `rbi/`. NEVER read `rbi/stripe.rbi`, since it's a huge file that collects data already present in other `.rbi` files
+
+## Generated Code
+
+- Files containing `File generated from our OpenAPI spec` at the top are generated; do not edit. Similarly, any code block starting with `The beginning of the section generated from our OpenAPI spec` is generated and should not be edited directly.
+  - If something in a generated file/range needs to be updated, add a summary of the change to your report but don't attempt to edit it directly.
+- Resource classes under `lib/stripe/resources/` are largely generated.
+- `stripe_client.rb`, `connection_manager.rb`, and core infrastructure files are NOT generated.
+
+## Conventions
+
+- Uses Ruby's standard `Net::HTTP` library
+- Bundler for gem management
+- Rubocop for style enforcement
+- Sorbet for optional type checking
+- Work is not complete until `just test` and `just typecheck` complete successfully.
+- All code must run on all supported Ruby versions (full list in the test section of @.github/workflows/ci.yml)
+
+### Comments
+
+- Comments MUST only be used to:
+    1. Document a function
+    2. Explain the WHY of a piece of code
+    3. Explain a particularly complicated piece of code
+- Comments NEVER should be used to:
+    1. Say what used to be there. That's no longer relevant!
+    2. Explain the WHAT of a piece of code (unless it's very non-obvious)
+
+It's ok not to put comments on/in a function if their addition wouldn't meaningfully clarify anything.