update doc

tests/scheduler/pbs/README.txt

@@ -1,3 +1,14 @@
-Use "test_pbs_wrapper.sh" script to test PBS wrapper code
-located in ../../../conf/scripts/scheduler
+Script to test PBS wrapper code
 
+You may have to adapt queue before running the test script:
+export MQUEUE=<your-queue>
+
+It is also possible to run an additional test by settings these
+variables before running the test script:
+
+export BDM_SCHEDULER="pbs"      # Optional since we force use of pbs
+export BDM_PLATFORM="ifremer"   # To load a specific conf file located in ../../../conf/scripts/scheduler/
+export BDM_QSTAT_CMD="ssh $DM_BDM_PBS_USER qstat"  # to change calling command for qstat
+export BDM_QSUB_CMD="ssh $DM_BDM_PBS_USER qsub"    # same for qsub
+
+These variables are loaded by ../../../conf/scripts/scheduler/pbs_wrapper.sh