more mapping and doc update for gitlinker

lua/config/git-linker.lua

@@ -13,3 +13,13 @@ keymap.set({ "n", "v" }, "<leader>gl", "", {
     gitlinker.get_buf_range_url(mode)
   end,
 })
+
+keymap.set("n", "<leader>gb", "", {
+  silent = true,
+  desc = "browse repo in browser",
+  callback = function()
+    gitlinker.get_repo_url({
+      action_callback = gitlinker.actions.open_in_browser
+    })
+  end
+})