build: add Makefile with docs (Hugo) and astro dev-server targets

Author: dcmcand

Makefile

@@ -0,0 +1,14 @@
+# Documentation site dev servers.
+#
+#   make docs    - run the Hugo docs site (docs/site) dev server
+#   make astro   - run the Astro docs site (docs/astro) dev server
+#
+# The two sites are a bake-off: both read the same content in docs/site/content.
+
+.PHONY: docs astro
+
+docs:
+	cd docs/site && hugo server
+
+astro:
+	cd docs/astro && { [ -d node_modules ] || npm install; } && npm run dev