[jdk11u-dev] RFR: 8343474: [updates] Customize README.md to specifics of update project

[Antonio Vieiro]

Backport of [JDK-8343474](https://bugs.openjdk.org/browse/JDK-8343474).

All links checked.

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Commit messages:
 - Backport ac1f86887384f0e3cf9becdeb9ee1e54fd4e60cb

Changes: https://git.openjdk.org/jdk11u-dev/pull/2978/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2978&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343474
  Stats: 8 lines in 1 file changed: 7 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2978.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2978/head:pull/2978

PR: https://git.openjdk.org/jdk11u-dev/pull/2978