docs: Update and split Contribution docs. (#122)

Co-authored-by: Atif Ali <atif@coder.com>

MAINTAINER.md

@@ -0,0 +1,103 @@
+# Maintainer Guide
+
+Quick reference for maintaining the Coder Registry repository.
+
+## Setup
+
+Install Go for README validation:
+
+```bash
+# macOS
+brew install go
+
+# Linux
+sudo apt install golang-go
+```
+
+## Daily Tasks
+
+### Review PRs
+
+Check that PRs have:
+
+- [ ] All required files (`main.tf`, `main.test.ts`, `README.md`)
+- [ ] Proper frontmatter in README
+- [ ] Working tests (`bun test`)
+- [ ] Formatted code (`bun run fmt`)
+- [ ] Avatar image for new namespaces (`avatar.png` or `avatar.svg` in `.images/`)
+
+#### Version Guidelines
+
+When reviewing PRs, ensure the version change follows semantic versioning:
+
+- **Patch** (1.2.3 → 1.2.4): Bug fixes
+- **Minor** (1.2.3 → 1.3.0): New features, adding inputs
+- **Major** (1.2.3 → 2.0.0): Breaking changes (removing inputs, changing types)
+
+PRs should clearly indicate the version change (e.g., `v1.2.3 → v1.2.4`).
+
+### Validate READMEs
+
+```bash
+go build ./cmd/readmevalidation && ./readmevalidation
+```
+
+## Releases
+
+### Create Release Tags
+
+After merging a PR:
+
+1. Get the new version from the PR (shown as `old → new`)
+2. Checkout the merge commit and create the tag:
+
+```bash
+# Checkout the merge commit
+git checkout MERGE_COMMIT_ID
+
+# Create and push the release tag using the version from the PR
+git tag -a "release/$namespace/$module/v$version" -m "Release $namespace/$module v$version"
+git push origin release/$namespace/$module/v$version
+```
+
+Example: If PR shows `v1.2.3 → v1.2.4`, use `v1.2.4` in the tag.
+
+### Publishing
+
+Changes are automatically published to [registry.coder.com](https://registry.coder.com) after tags are pushed.
+
+## README Requirements
+
+### Module Frontmatter (Required)
+
+```yaml
+display_name: "Module Name"
+description: "What it does"
+icon: "../../../../.icons/tool.svg"
+maintainer_github: "username"
+partner_github: "partner-name" # Optional - For official partner modules
+verified: false # Optional - Set by maintainers only
+tags: ["tag1", "tag2"]
+```
+
+### Namespace Frontmatter (Required)
+
+```yaml
+display_name: "Your Name"
+bio: "Brief description of who you are and what you do"
+avatar_url: "./.images/avatar.png"
+github: "username"
+linkedin: "https://www.linkedin.com/in/username" # Optional
+website: "https://yourwebsite.com" # Optional
+support_email: "you@example.com" # Optional
+status: "community" # or "partner", "official"
+```
+
+## Common Issues
+
+- **README validation fails**: Check YAML syntax, ensure h1 header after frontmatter
+- **Tests fail**: Ensure Docker with `--network=host`, check Terraform syntax
+- **Wrong file structure**: Use `./scripts/new_module.sh` for new modules
+- **Missing namespace avatar**: Must be `avatar.png` or `avatar.svg` in `.images/` directory
+
+That's it. Keep it simple.