docs: track CONTRIBUTING.md past the internal-markdown ignore

.gitignore

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 # Ignore internal docs/markdown
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+!CONTRIBUTING.md
 
 # Ignore log and debug artifacts
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CONTRIBUTING.md

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+# Contributing to BYOC
+
+Contributions are welcome. Bug reports, fixes, new provider support, documentation, and tests are all useful. There is no contributor license agreement to sign. By opening a pull request you agree that your contribution is licensed under the project's [MIT license](LICENSE).
+
+## Reporting bugs and requesting features
+
+Open an issue and include:
+
+- Your operating system and Obsidian version
+- The BYOC version (shown in Settings under Community plugins)
+- The remote provider involved, and whether encryption (a password) is enabled
+- Steps to reproduce, and what you expected versus what happened
+
+Do not paste credentials, tokens, or other secrets into an issue.
+
+## Development setup
+
+```bash
+git clone https://github.com/winters27/obsidian-byoc
+cd obsidian-byoc
+npm install
+npm run build   # bundles main.js, manifest.json, styles.css into the repo root
+npm test        # runs the test suite
+```
+
+`npm run build` also copies the three build outputs into a local Obsidian plugin folder if one is configured, so you can reload Obsidian (Ctrl/Cmd+R) and try your change against a real vault.
+
+To test OAuth providers with your own credentials, copy `.env.example.txt` to `.env` and fill in the relevant `*_CLIENT_ID` / `*_CLIENT_SECRET` values before building.
+
+## Project layout
+
+- `src/sync/` — the 3-way merge engine. `planner.ts` decides push/pull/delete/conflict for each file, `syncer.ts` orders and executes those decisions, `conflict.ts` builds conflict copies.
+- `src/fs*.ts` — one file system adapter per provider (for example `fsWebdav.ts`, `fsS3.ts`), all behind a common interface.
+- `src/fsEncrypt.ts` — the encryption layer that wraps any provider with rclone-crypt or OpenSSL encryption.
+- `src/settings*.ts` — the settings UI, with one panel per provider.
+- `tests/` — the test suite, run with `npm test`.
+
+## Pull requests
+
+1. Fork the repository and create a branch off `master`.
+2. Keep each pull request focused on one change.
+3. Add or update tests when you change sync behavior. The decision matrix in `src/sync/planner.ts` is covered by `tests/syncPlanner.test.ts`; a sync logic change without a matching test is hard to review.
+4. Run `npm test` and `npm run build` before pushing.
+5. Describe the problem and the fix in the pull request, and link any related issue.
+
+## Code style
+
+Formatting is handled by Biome and linting by ESLint:
+
+```bash
+npm run format   # apply formatting
+npm run lint     # check for lint issues
+```
+
+Match the style of the surrounding code rather than introducing new conventions.