git: openjdk/amber-docs: Polish makefile: Remove noise from build log, add README.html, make file detection more robust

[John Rose]

Changeset: 16ad1dd7
Author:    John Rose <jrose at openjdk.org>
Date:      2021-04-21 16:19:53 +0000
URL:       https://git.openjdk.java.net/amber-docs/commit/16ad1dd7

Polish makefile: Remove noise from build log, add README.html, make file detection more robust

! Makefile