Add lockdown mode to docs

Author: JoannaaKL

README.md

@@ -1256,6 +1256,25 @@ docker run -i --rm \
   ghcr.io/github/github-mcp-server
 ```
 
+## Lockdown Mode
+
+Lockdown mode limits the content that the server will surface from public repositories. When enabled, requests that fetch issue details will return an error if the issue was created by someone who does not have push access to the repository. Private repositories are unaffected, and collaborators can still access their own issues.
+
+```bash
+./github-mcp-server --lockdown-mode
+```
+
+When running with Docker, set the corresponding environment variable:
+
+```bash
+docker run -i --rm \
+  -e GITHUB_PERSONAL_ACCESS_TOKEN=<your-token> \
+  -e GITHUB_LOCKDOWN_MODE=1 \
+  ghcr.io/github/github-mcp-server
+```
+
+At the moment lockdown mode applies to the issue read toolset, but it is designed to extend to additional data surfaces over time.
+
 ## i18n / Overriding Descriptions
 
 The descriptions of the tools can be overridden by creating a

docs/installation-guides/README.md

@@ -94,4 +94,5 @@ After installation, you may want to explore:
 - **Toolsets**: Enable/disable specific GitHub API capabilities
 - **Read-Only Mode**: Restrict to read-only operations
 - **Dynamic Tool Discovery**: Enable tools on-demand
+- **Lockdown Mode**: Hide public issue details created by non-collaborators