add instructions to live reload docs

CONTRIBUTING.md

@@ -0,0 +1,21 @@
+# Contributing to cLAN
+
+## Live-reloading documentation
+
+Enter the `docs` directory:
+
+```shell-session
+cd docs
+```
+
+Enter the development shell or enable `direnv`:
+
+```shell-session
+direnv allow
+```
+
+Run a local server:
+
+```shell-session
+mkdocs serve
+```