RFR: Update README.md to be used as Release Notes for Leyden EA 2

[Ioi Lam]

In Leyden EA 1, we used a special version of README.md as the release nodes:

https://jdk.java.net/leyden/ -> [Release Notes](https://github.com/openjdk/leyden/blob/leyden-ea1-release-notes/README.md)

As we are releasing Leyden EA 2, we will use the same process for the release notes.

- The README.md is taken from the [GIT version of Leyden EA 2 candidate](https://github.com/openjdk/leyden/commit/ffacb36e564b24e335b11fe5be8e574dffac2055) (as of today).
- Removed information about building and benchmarks
- Removed mentions of AOT features that have already been integrated into the mainline.
- Updated the terminology from "CDS" to "AOT"

A rendered version of this document can be found here:
- https://github.com/iklam/leyden/blob/leyden-ea2-release-notes/README.md

(I will merge some of the above changes back to leyden/premain branch after this PR is integrated).

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Commit messages:
 - Fixed whitespaces
 - more edits
 - More edits
 - Updated README.md for Leyden EA 2 Release

Changes: https://git.openjdk.org/leyden/pull/92/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=92&range=00
  Stats: 453 lines in 2 files changed: 20 ins; 394 del; 39 mod
  Patch: https://git.openjdk.org/leyden/pull/92.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/92/head:pull/92

PR: https://git.openjdk.org/leyden/pull/92