docs(container): add README explaining server container configuration and registry

Author: observerw

container/README.md

@@ -0,0 +1,123 @@
+# Container Registry
+
+This directory contains Docker container configurations for LSP servers and a registry system for managing server versions.
+
+## Directory Structure
+
+```
+container/
+├── registry.toml           # Server registry configuration
+├── registry.schema.json    # JSON schema for registry validation
+└── <server-name>/          # Individual server configurations
+    └── ContainerFile       # Docker container build instructions
+```
+
+## Adding a New LSP Server
+
+To add a new LSP server, you need to:
+
+1. Create a directory for the server
+2. Create a `ContainerFile` with build instructions
+3. Register the server in `registry.toml`
+
+### Step 1: Create Server Directory and ContainerFile
+
+Create a new directory with the server name and add a `ContainerFile`:
+
+```dockerfile
+# Example ContainerFile for a Node.js based LSP server
+ARG VERSION=1.0.0
+FROM node:22-slim AS builder
+ARG VERSION
+RUN npm install -g <package-name>@${VERSION}
+
+FROM node:22-slim
+ARG VERSION
+LABEL org.opencontainers.image.version="${VERSION}"
+COPY --from=builder /usr/local/lib/node_modules /usr/local/lib/node_modules
+COPY --from=builder /usr/local/bin/<binary-name> /usr/local/bin/<binary-name>
+
+WORKDIR /workspace
+ENTRYPOINT ["<binary-name>", "--stdio"]
+```
+
+**Key points:**
+- Use multi-stage builds to minimize final image size
+- Define `ARG VERSION` for version management
+- Set appropriate labels for metadata
+- Use `--stdio` for LSP protocol communication
+- Ensure the ENTRYPOINT runs the language server
+
+### Step 2: Register in Registry
+
+Add an entry to `registry.toml`:
+
+```toml
+[server-name]
+type = "npm"        # or "pypi", "github", "custom"
+package = "package-name"  # for npm/pypi
+repo = "owner/repo"       # for github
+strip_v = true      # optional, remove 'v' prefix from github releases
+```
+
+#### Registry Types
+
+**npm**: For Node.js packages
+```toml
+[typescript]
+type = "npm"
+package = "typescript-language-server"
+```
+
+**pypi**: For Python packages
+```toml
+[pyrefly]
+type = "pypi"
+package = "pyrefly"
+```
+
+**github**: For GitHub releases
+```toml
+[rust-analyzer]
+type = "github"
+repo = "rust-lang/rust-analyzer"
+
+[deno]
+type = "github"
+repo = "denoland/deno"
+strip_v = true  # Remove 'v' prefix from version tags
+```
+
+**custom**: For custom version checking commands
+```toml
+[custom-server]
+type = "custom"
+command = "curl -s https://api.example.com/version | jq -r .version"
+```
+
+### Step 3: Build and Test
+
+The CI system will automatically:
+1. Check for new versions using the registry configuration
+2. Build containers when versions change
+3. Push images to the registry
+
+To manually test:
+```bash
+# Build container
+docker build -f container/<server-name>/ContainerFile -t lsp/<server-name>:latest .
+
+# Test the container
+docker run --rm lsp/<server-name>:latest --version
+```
+
+## Version Management
+
+Versions are automatically updated via the `update_containers.yml` GitHub workflow:
+
+1. `scripts/server_versions.py` reads `registry.toml` and fetches latest versions
+2. Updates `ContainerFile` ARG VERSION values
+3. Builds and pushes new container images
+4. Commits version updates back to the repository
+
+The workflow runs weekly or can be triggered manually with the "force" option.