[jdk21u-dev] RFR: 8343474: [updates] Customize README.md to specifics of update project [v3]

[Goetz Lindenmaier]

> Customize the README.md to jdk21u.
> 
> Plan is to backport this to 17 and maybe older jdks and adapt the paths etc correspondingly.
> So let’s keep this sufficiently generic so that the information holds for jdkXu and jdkXu-dev
> and that the change can easily be backported (by adapting 21->17 etc).
> 
> Should we put there more information?

Goetz Lindenmaier has updated the pull request incrementally with one additional commit since the last revision:

  Taking over suggestion of Andrew
  
  Yes, this makes it much clearer.  Thanks!
  
  Co-authored-by: Andrew Haley <aph-open at littlepinkcloud.com>

-------------

Changes:
  - all: https://git.openjdk.org/jdk21u-dev/pull/1118/files
  - new: https://git.openjdk.org/jdk21u-dev/pull/1118/files/bc062ce9..f253b707

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1118&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1118&range=01-02

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1118.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1118/head:pull/1118

PR: https://git.openjdk.org/jdk21u-dev/pull/1118