Repository navigation

Added BTN-1 GPIO pinout page #339

	name: Restrict PRs to main
	on:
	pull_request:
	branches: [main]
	jobs:
	check-source:
	runs-on: ubuntu-latest
	steps:
	- name: Verify source is dev
	run: \|
	if [ "${{ github.head_ref }}" != "dev" ]; then
	echo "::error::PRs to main must come from 'dev'. Got: ${{ github.head_ref }}"
	exit 1
	fi