Add docs and git hooks

docs/linking.md

@@ -10,3 +10,30 @@ matrix-js-sdk: ../path/to/matrix-js-sdk
 ```
 
 Then run `yarn install`.
+
+## Hooks
+
+Changes in `.links.yaml` will also update `yarn.lock` when `yarn` is executed. The lockfile will then contain the local
+version of the package which would not work on others dev setups or the github CI.
+One always needs to run:
+
+```bash
+mv .links.yaml .links.disabled.yaml
+yarn
+```
+
+before committing a change.
+
+To make it more convenient to work with this linking system we added git hooks for your conviniece.
+A `pre-commit` hook will run `mv .links.yaml .links.disabled.yaml`, `yarn` and `git add yarn.lock` if it detects
+a `.links.yaml` file and abort the commit.
+You will than need to check if the resulting changes are appropriate and commit again.
+
+A `post-commit` hook will setup the linking as it was
+before if a `.links.disabled.yaml` is present. It runs `mv .links.disabled.yaml .links.yaml` and `yarn`.
+
+To activate the hooks automatically configure git with
+
+```bash
+git config --local core.hooksPath .githooks/
+```