build: add doc linting when runnning make lint

Fixes: #18466

PR-URL: #18472
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

Makefile

@@ -1183,6 +1183,7 @@ lint: ## Run JS, C++, MD and doc linters.
 	$(MAKE) lint-js || EXIT_STATUS=$$? ; \
 	$(MAKE) lint-cpp || EXIT_STATUS=$$? ; \
 	$(MAKE) lint-addon-docs || EXIT_STATUS=$$? ; \
+	$(MAKE) lint-md || EXIT_STATUS=$$? ; \
 	exit $$EXIT_STATUS
 CONFLICT_RE=^>>>>>>> [0-9A-Fa-f]+|^<<<<<<< [A-Za-z]+