Put default memory to mem spec

Author: hajgato

mkdocs/docs/HPC/fine_tuning_job_specifications.md

@@ -295,6 +295,15 @@ or on the command line
 qsub -l mem=4gb
 ```
 
+{% if site==gent %}
+If you do not request memory (neither in the job script nor on the command line), the default memory
+that your job will get access is the proportional share of the total memory on the node:
+If you request a full node, all memory will be available.
+If you request `N` cores on a cluster where nodes have `M` cores, you will get `N/M`
+of the total memory on the node. For the number of cores and available memory per cluster, please see our
+[infrastructure](https://www.ugent.be/hpc/en/infrastructure).
+{% endif %}
+
 {% if site!=gent %}
 This setting is ignored if the number of nodes is not 1.