Add docs command to build and serve documentation

Makefile

@@ -13,6 +13,10 @@ export
 help:
 	@awk 'BEGIN {FS = " ?#?: "; print ""${ANKI_SERVER_NAME}" "${ANKI_SERVER_VERSION}"\n"${ANKI_SERVER_DESCRIPTION}"\n\nUsage: make \033[36m<command>\033[0m\n\nCommands:"} /^.PHONY: ?[a-zA-Z_-]/ { printf "  \033[36m%-10s\033[0m %s\n", $$2, $$3 }' $(MAKEFILE_LIST)
 
+.PHONY: docs #: Build and serve documentation.
+docs: print-env
+	@${MKDOCS} ${MKDOCS_OPTION} -f docs/mkdocs.yml
+
 %:
 	@test -f scripts/${*}.sh
 	@${SHELL} scripts/${*}.sh