Add remotes.<group> as planned feature for remotes (#450)

Author: Byron

src/plumbing/progress.rs

@@ -261,6 +261,12 @@ static GIT_CONFIG: &[Record] = &[
             deviation: None,
         },
     },
+    Record {
+        config: "remotes.<group>",
+        usage: Planned {
+            note: Some("useful for multi-remote fetches as part of the standard API, maybe just `group(name) -> Option<Vec<Remote>>`"),
+        },
+    },
     Record {
         config: "url.<base>.insteadOf",
         usage: InModule {