git-prune: add page (#4696)

pages/common/git-prune.md

@@ -0,0 +1,17 @@
+# git prune
+
+> Git command for pruning all unreachable objects from the object database.
+> This command is often not used directely but as an internal command that is used by git gc.
+> More information: <https://git-scm.com/docs/git-prune>.
+
+- Report what would be removed by git prune without removing it:
+
+`git prune --dry-run`
+
+- Prune unreachable objects and display what has been pruned to `stdout`:
+
+`git prune --verbose`
+
+- Prune unreachable objects while showing progress:
+
+`git prune --progress`