Update slurm-job-submission-and-execution.md

docs.it4i/general/slurm-job-submission-and-execution.md

@@ -128,6 +128,8 @@ $ set | grep ^SLURM
 
 #### Useful Variables
 
+Commonly used variables are:
+
 | variable name | description | example |
 | ------ | ------ | ------ |
 | SLURM_JOBID | job id of the executing job| 593 |