remote doc: document long forms of set-head options

"git remote set-head" has always supported --add and --delete
as synonyms for the -a and -d option but forgot to document
them.

Signed-off-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

Documentation/git-remote.txt

@@ -13,7 +13,7 @@ SYNOPSIS
 'git remote add' [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=<fetch|push>] <name> <url>
 'git remote rename' <old> <new>
 'git remote remove' <name>
-'git remote set-head' <name> (-a | -d | <branch>)
+'git remote set-head' <name> (-a | --auto | -d | --delete | <branch>)
 'git remote set-branches' [--add] <name> <branch>...
 'git remote set-url' [--push] <name> <newurl> [<oldurl>]
 'git remote set-url --add' [--push] <name> <newurl>
@@ -101,9 +101,9 @@ branch. For example, if the default branch for `origin` is set to
 `master`, then `origin` may be specified wherever you would normally
 specify `origin/master`.
 +
-With `-d`, the symbolic ref `refs/remotes/<name>/HEAD` is deleted.
+With `-d` or `--delete`, the symbolic ref `refs/remotes/<name>/HEAD` is deleted.
 +
-With `-a`, the remote is queried to determine its `HEAD`, then the
+With `-a` or `--auto`, the remote is queried to determine its `HEAD`, then the
 symbolic-ref `refs/remotes/<name>/HEAD` is set to the same branch. e.g., if the remote
 `HEAD` is pointed at `next`, "`git remote set-head origin -a`" will set
 the symbolic-ref `refs/remotes/origin/HEAD` to `refs/remotes/origin/next`. This will