fix: output hint on failure

Signed-off-by: Michael Nahkies <michael@nahkies.co.nz>

Author: mnahkies

Makefile

@@ -322,7 +322,8 @@ lint: gradle-dependencies ## Format the Android code
 
 .PHONY: lint-ci
 lint-ci: gradle-dependencies ## Check the Android code is formatted
-	(cd android && ./gradlew ktfmtCheck)
+	(cd android && ./gradlew ktfmtCheck) \
+	|| (echo -e "\033[1;31mLint failed. Run 'make lint' to fix.\033[0m" && exit 1)
 
 .PHONY: emulator
 emulator: ## Start an android emulator instance