Add LFS timeout issue to troubleshooting doc (#5129)

Author: ravenscroftj

docs/content/doc/help/troubleshooting.en-us.md

@@ -80,3 +80,17 @@ To migrate an repository *with* all tags you need to do two things
  ```
  gitea admin repo-sync-releases
  ```
+
+## LFS Issues
+
+For issues concerning LFS data upload
+
+```
+batch response: Authentication required: Authorization error: <GITEA_LFS_URL>/info/lfs/objects/batch                                                                                                              
+Check that you have proper access to the repository
+error: failed to push some refs to '<GIT_REPO_URL>'
+```
+Have you checked the value of `LFS_HTTP_AUTH_EXPIRY` in your `app.ini` file? By default your LFS token will expire after 20 minutes. If you have a slow connection or a large file (or both) it may not finish uploading within the time limit. 
+
+You may want to set this value to `60m` or `120m`.
+