Add better Swagger description and a example for GetArchive (#12743)

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

templates/swagger/v1_json.tmpl

@@ -2075,7 +2075,7 @@
           },
           {
             "type": "string",
-            "description": "archive to download, consisting of a git reference and archive",
+            "description": "the git reference for download with attached archive format (e.g. master.zip)",
             "name": "archive",
             "in": "path",
             "required": true