Improve pgindent release workflow.

Update RELEASE_CHANGES to direct the reader towards completing the steps
outlined in the pgindent README, both as a pre-beta task and as a task
to be performed when starting a new development cycle.

This makes it less likely that somebody will miss updating the
.git-blame-ignore-revs file when running pgindent against the tree as a
routine release change task.

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAH2-Wz=2PjF4As8dWECArsXxLKganYmQ-s0UeGqHHbHhqDKqeA@mail.gmail.com

src/tools/RELEASE_CHANGES

@@ -70,11 +70,7 @@ but there may be reasons to do them at other times as well.
 
 * Run mechanical code beautification tools:
   pgindent, pgperltidy, and "make reformat-dat-files"
-  (see src/tools/pgindent/README)
-
-* Update .git-blame-ignore-revs. It should contain all of the newly
-  created code beautification commits.  Make sure that you use
-  full-length commit hashes for this.
+  (complete steps from src/tools/pgindent/README)
 
 * Renumber any manually-assigned OIDs between 8000 and 9999
   to lower numbers, using renumber_oids.pl (see notes in bki.sgml)
@@ -90,7 +86,7 @@ Starting a New Development Cycle
 ================================
 
 * Typically, we do pgindent and perltidy runs just before branching,
-  as well as before beta
+  as well as before beta (complete steps from src/tools/pgindent/README)
 
 * Create a branch in git for maintenance of the previous release
 	o on master branch, do:

src/tools/pgindent/README

@@ -82,7 +82,8 @@ you used.
 
 4) Add the newly created commits to the .git-blame-ignore-revs file so
    that "git blame" ignores the commits (for anybody that has opted-in
-   to using the ignore file).
+   to using the ignore file).  Follow the instructions that appear at
+   the top of the .git-blame-ignore-revs file.
 
 Another "git commit" will be required for your ignore file changes.