RFR: Update README.md to be used as Release Notes for Leyden EA 2 [v2]

[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).

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  Added info about CPU matches and diagnosing loading errors; fixed typos

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

Changes:
  - all: https://git.openjdk.org/leyden/pull/92/files
  - new: https://git.openjdk.org/leyden/pull/92/files/0e48e150..797f383c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=leyden&pr=92&range=01
 - incr: https://webrevs.openjdk.org/?repo=leyden&pr=92&range=00-01

  Stats: 23 lines in 1 file changed: 20 ins; 0 del; 3 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