move shmem from FAQ to trouble shooting

docs/faq/README.md

@@ -38,9 +38,3 @@ Hyperloop trains have a so-called express train feature. This feature is based o
 ### Why is it that my train test has a CPU warning but my wagon test was fine?
 
 This usually happens in a situation where the wagon test (which runs on a single core) uses so much memory that it doesn't fit a single core job on the grid and therefore needs two cores for the train (more cores means a higher memory allowance). But if the devices in the wagon cannot be parallelised well over multiple cores, this leads to more wall time and a higher CPU usage as the cores will be underutilised. In this situation, one can either reduce the wagon memory consumption to fit into a single core or reduce the CPU consumption to fit the dataset. 
-
-## Your local machines
-### `shmem: could not create a message of size ...`
-
-Add `--shm-segment-size 1000000000` (or larger number) to your o2 command.
-It is due to shared memory segment that is probably outdated for the size of the intermediate tables you have. It is actually set as 90% of system's max VSIZE allowance set in limits, or 2GB if the limits cannot be found, which is probably what happens in your case.

docs/troubleshooting/README.md

@@ -180,6 +180,11 @@ Error in <TJAlienConnectionManager>: Failed to connect to any server! Giving up
 - You should be greeted with `Welcome to the ALICE GRID`.
 - Exit with `exit`.
 
+### shmem: could not create a message of size ...
+
+Add `--shm-segment-size 1000000000` (or larger number) to your o2 command.
+It is due to shared memory segment that is probably outdated for the size of the intermediate tables you have. It is actually set as 90% of system's max VSIZE allowance set in limits, or 2GB if the limits cannot be found, which is probably what happens in your case.
+
 ## Graphical issue with high DPI monitors
 
 When using monitors with high DPI the labels and text in TBrowser might be too small, especially when fractional scaling is enabled in multiple