Add sha512 into the release vote mail

[wu-sheng]

In the beta release vote:

> Release Candidate:
> *https://dist.apache.org/repos/dist/dev/incubator/skywalking/5.0.0-beta/


I strongly recommend using suffixes like -RC1 in the release candidate
URL and tag -- how do voters (and anyone checking the vote later) know if you
happened to make a 'second 5.0.0-beta' release candidate?  

For that reason the VOTE email should also include 
svn revision number from dist.apache.org, and/oor sha checksum of the
files under vote.  

Assuming r26864 (from "svn log") aka sha512 checksums

33b13cc7bc4ddea46d727ed8910c54c2e3b9acd6614a7f937e01e34ae6403942791ec3505d16de674605c665a4c0805271eb90a94775701d941462c530a99d11  apache-skywalking-apm-incubating-5.0.0-beta-src.tgz
770ad70ad3e23fbd93ea675528a81735848a92557f91036b23652b4c2a0282a7198bf9a09fd4570f8bef180d956e81e4f93a9c2308106de1b3d815feeb0dfd84  apache-skywalking-apm-incubating-5.0.0-beta.tar.gz
d4ca36ed94a6d3557b747fe3ba3daf1dee5dca6d0f827af404762344c41214b4e5ff2173536e6c2feac383d9d0bdbaa648a5f0b8eee9f1b0913734d2c5adfffa  apache-skywalking-apm-incubating-5.0.0-beta.zip

Make the adjustments in release doc.

• Add sha512 text into the mail Release Candidate: section.

[wu-sheng]

Provided