[web] Added workaround for git-lfs push errors.

web/content/docs/devguide/troubleshooting/git.pandoc

@@ -14,3 +14,27 @@ weight = 1044
 If you have any Git-related questions first look at these links:
 
 - [Git Flight Rules](https://github.com/k88hudson/git-flight-rules)
+
+
+## Git-LFS issues
+
+### *The system cannot find the file specified.*
+
+Example error output:
+
+```bash
+open C:\data\code\ogs6\ogs\Tests\Data\Mechanics\Ehlers\ref_axisymmetric_sphere_pcs_0_ts_100_t_1.000000.vtu: The system cannot find the file specified.
+error: failed to push some refs to 'git@github.com:bilke/ogs.git'
+```
+
+Solution:
+
+Fetch all lfs files from `ufz/ogs` and push them to your remote.
+
+```bash
+# this downloads ALL lfs objects from the old lfs server
+git lfs fetch --all origin # or upstream, this should point to ufz/ogs
+
+# pushes ALL lfs objects to the new lfs server
+git lfs push --all my-remote # this should point to your remote
+```