Update path to the generate symbols script, and expand the start of release doc.
------------- Commit messages: - doc updates Changes: https://git.openjdk.org/jdk/pull/28606/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28606&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8372940 Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod Patch: https://git.openjdk.org/jdk/pull/28606.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/28606/head:pull/28606 PR: https://git.openjdk.org/jdk/pull/28606
