Doc: Add description to request_dark script

@haufs A small description of request_dark script is added. Script is located at /gpfs/exfel/data/scratch/haufs/request_darks.py. Description is based on the help message and my guess.

docs/source/advanced.rst

@@ -5,6 +5,32 @@ Advanced Topics
 
 The following tasks should only be carried out by trained staff.
 
+Request dark characterization
+-----------------------------
+
+Script runs dark characterization notebook with default parameters via web service. Data needs to be transferred via the MDC, however, the web service will wait for this transfer to be completed. Detector is chosen automatically with respect to given instrument (`--instrument`). For AGIPD, LPD, Jungfrau runs for the three gain stages need to be given (`--run-high`, `--run-med`, `--run-low`). For FastCCD and ePIX only a single run needs to be given (`--run`).
+
+Complete list of parameters is::
+
+  -h, --help            show this help message and exit
+  --proposal PROPOSAL   The proposal number, without leading p, but with
+                        leading zeros
+  --instrument {SPB,MID,FXE,SCS,SQS,HED}
+                        The instrument
+  --cycle CYCLE         The facility cycle
+  --run-high RUN_HIGH   Run number of high gain data as an integer
+  --run-med RUN_MED     Run number of medium gain data as an integer
+  --run-low RUN_LOW     Run number of low gain data as an integer
+  --run RUN             Run number as an integer
+
+
+Path to data files is defined from script parameters. A typical data path, which can be found in the MDC is::
+
+/gpfs/exfel/exp/MID/201930/p900071/raw
+
+Where `MID` is an instrument name, `201930` is a cycle, `900071` is a proposal number.
+
+
 Initiating Automated Offline Correction
 ---------------------------------------
 

[Steffen Hauf]

The script, the data,

for any transfers

The detector

The complete list

The path

[Steffen Hauf]

The script, the data,

for any transfers

The detector

The complete list

The path

[Mikhail Karnevskiy]

Done.