revisions.txt: use description list for special refs

The special refs listed in 'gitrevisions' (under the '<refname>' entry)
are on separate lines in the Asciidoc source, but end up as a single
continuous paragraph in the rendered documentation (see e.g. [1]). In
following commits we will mention additional special refs, so to improve
legibility, use a description list such that every entry appears on its
own line. Since we are already in a description list, use ':::' as the
term delimiter.

In order for the new description list to be aligned with the description
under the '<refname>' entry, instead of being aligned with the last
entry of the "in the following rules" nested list, use the "ancestor
list continuation" syntax [2], i.e., leave an empty line before the
continuation '+'. Do the same for the paragraph following the new
description list ("Note that any...").

While at it, also use a continuation '+' before the "in the following
rules" list, for correctness. The parser seems not to care here, but
it's best to keep the sources correct.

[1] https://git-scm.com/docs/gitrevisions#Documentation/gitrevisions.txt-emltrefnamegtemegemmasterememheadsmasterememrefsheadsmasterem
[2] https://docs.asciidoctor.org/asciidoc/latest/lists/continuation/#ancestor-list-continuation

Suggested-by: Victoria Dye <[email protected]>
Based-on-patch-by: Taylor Blau <[email protected]>
Signed-off-by: Philippe Blain <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: phil-blain

Documentation/revisions.txt

@@ -30,7 +30,7 @@ characters and to avoid word splitting.
   explicitly say 'heads/master' to tell Git which one you mean.
   When ambiguous, a '<refname>' is disambiguated by taking the
   first match in the following rules:
-
++
   . If '$GIT_DIR/<refname>' exists, that is what you mean (this is usually
     useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD`, `MERGE_HEAD`
     and `CHERRY_PICK_HEAD`);
@@ -44,19 +44,25 @@ characters and to avoid word splitting.
   . otherwise, 'refs/remotes/<refname>' if it exists;
 
   . otherwise, 'refs/remotes/<refname>/HEAD' if it exists.
+
 +
-`HEAD` names the commit on which you based the changes in the working tree.
-`FETCH_HEAD` records the branch which you fetched from a remote repository
-with your last `git fetch` invocation.
-`ORIG_HEAD` is created by commands that move your `HEAD` in a drastic
-way (`git am`, `git merge`, `git rebase`, `git reset`),
-to record the position of the `HEAD` before their operation, so that
-you can easily change the tip of the branch back to the state before you ran
-them.
-`MERGE_HEAD` records the commit(s) which you are merging into your branch
-when you run `git merge`.
-`CHERRY_PICK_HEAD` records the commit which you are cherry-picking
-when you run `git cherry-pick`.
+  `HEAD`:::
+    names the commit on which you based the changes in the working tree.
+  `FETCH_HEAD`:::
+    records the branch which you fetched from a remote repository with
+    your last `git fetch` invocation.
+  `ORIG_HEAD`:::
+    is created by commands that move your `HEAD` in a drastic way (`git
+    am`, `git merge`, `git rebase`, `git reset`), to record the position
+    of the `HEAD` before their operation, so that you can easily change
+    the tip of the branch back to the state before you ran them.
+  `MERGE_HEAD`:::
+    records the commit(s) which you are merging into your branch when you
+    run `git merge`.
+  `CHERRY_PICK_HEAD`:::
+    records the commit which you are cherry-picking when you run `git
+    cherry-pick`.
+
 +
 Note that any of the 'refs/*' cases above may come either from
 the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.