completion: support restore

Completion for restore is straightforward. We could still do better
though by giving the list of just tracked files instead of all present
ones. But let's leave it for later.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -2491,6 +2491,21 @@ _git_reset ()
 	__git_complete_refs
 }
 
+_git_restore ()
+{
+	case "$cur" in
+	--conflict=*)
+		__gitcomp "diff3 merge" "" "${cur##--conflict=}"
+		;;
+	--source=*)
+		__git_complete_refs --cur="${cur##--source=}"
+		;;
+	--*)
+		__gitcomp_builtin restore
+		;;
+	esac
+}
+
 __git_revert_inprogress_options="--continue --quit --abort"
 
 _git_revert ()