doc: create maintaining-brotli.md

PR-URL: #47380
Refs: nodejs/security-wg#828
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/contributing/maintaining-brotli.md

@@ -0,0 +1,26 @@
+# Maintaining brotli
+
+The [brotli](https://github.com/google/brotli) dependency is used for 
+the homonym generic-purpose lossless compression algorithm.
+
+## Updating brotli
+
+The `tools/dep_updaters/update-brotli.sh` script automates the update of the
+brotli source files.
+
+Check that Node.js still builds and tests.
+
+## Committing postject
+
+1. Add brotli:
+   ```console
+   $ git add deps/brotli
+   ```
+2. Commit the changes: `git commit`.
+3. Add a message like:
+
+   ```text
+   deps,test: update brotli to <version>
+
+   Updated as described in doc/contributing/maintaining-brotli.md.
+   ```