Makefile fix and only run src/README.md sync on change (#1393)

* update header (was using old one). Update makefile to only run the src/README.md update when the root README.md has changed.

* update makefile to only output message when src/README.md is regenerated

* simplify src/README.md generation by using intrinsic functionality of Makefile

* Update Makefile

Co-authored-by: Lio李歐 <[email protected]>

* Update Makefile for README.md sync to make sure users add src/README.md to commits

* Update Makefile

---------

Co-authored-by: Lio李歐 <[email protected]>

Author: nullfunc

Makefile

@@ -10,16 +10,17 @@ pre-commit:
 	@if git diff --cached --name-only | grep -q '^src/'; then make -C src lint; fi
 
 .PHONY: pre-push
-pre-push: sync-readme
+pre-push: src/README.md
 	@make -C src test
 
 setup:
 	go -C src mod tidy
 
-.PHONY: sync-readme
-sync-readme:
-	awk '/^## Develop Anything\. Deploy Anywhere\./{p=1} (/^## /||/^### /){if(p&&!/^## Develop Anything\. Deploy Anywhere\./){exit}} p' README.md > src/README.md; \
+src/README.md: README.md
+	@awk '/^## Develop Once\. Deploy Anywhere\./{p=1} (/^## /||/^### /){if(p&&!/^## Develop Once\. Deploy Anywhere\./){exit}} p' README.md > src/README.md; \
 	awk '/^## Defang CLI/{p=1} (/^## /||/^### /){if(p&&!/^## Defang CLI/){exit}} p' README.md >> src/README.md; \
 	awk '/^## Getting started/{p=1} (/^## /||/^### /){if(p&&!/^## Getting started/){exit}} p' README.md >> src/README.md; \
 	awk '/^## Support/{p=1} (/^## /||/^### /){if(p&&!/^## Support/){exit}} p' README.md >> src/README.md; \
-	awk '/^## Environment Variables/{p=1} (/^## /||/^### /){if(p&&!/^## Environment Variables/){exit}} p' README.md >> src/README.md
+	awk '/^## Environment Variables/{p=1} (/^## /||/^### /){if(p&&!/^## Environment Variables/){exit}} p' README.md >> src/README.md; \
+	@echo 'src/README.md was updated because root README.md changed. Please add src/README.md to your commit.';
+	@false