githooks: add docs prefix

In the process, update the README to point to how to add the githooks
folder. I had to go to aports to find the command.

Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7077>

.githooks/prepare-commit-msg

@@ -49,6 +49,12 @@ case "$lcp" in
 	device/*/*)
 		prefix="$(echo "$lcp" | cut -d/ -f3)"
 		;;
+	docs/*.adoc)
+		prefix="docs/$(basename $lcp .adoc)"
+		;;
+	docs/*)
+		prefix="docs"
+		;;
 	device/*)
 		# Multiple packages touched for same device category. More
 		# logic could be added to detect if they all belong to same

README.md

@@ -12,3 +12,12 @@ Helpful resources:
 * [Alpine Linux aports](https://gitlab.alpinelinux.org/alpine/aports/)
 * [Alpine Linux package search](https://pkgs.alpinelinux.org/packages)
 * [postmarketOS package search](https://pkgs.postmarketos.org/packages)
+
+## Git Hooks
+
+You can find some useful git hooks in the `.githooks` directory.
+To use them, run the following command after cloning this repository:
+
+```sh
+git config --local core.hooksPath .githooks
+```