[Anchor] Start explaining env variables

docs/o2dpgworkflow/anchored.md

@@ -89,6 +89,33 @@ ${O2DPG_ROOT}/MC/run/ANCHOR/anchorMC.sh
 
 In addition to the collision system, one can also influence other parameters, like in this case the centre-of-mass energy.
 
+## Environment variables
+
+The `anchorMC.sh` script is sensitive to the following environment variables. Please set/export them, especially in case they are required.
+
+| Variable | Required | Default | Comments |
+| -------- | -------- | ------- | -------- |
+| `ALIEN_JDL_LPMANCHORPASSNAME` | yes | | |
+| `ALIEN_JDL_MCANCHOR` | yes | | |
+| `ALIEN_JDL_LPMRUNNUMBER` | yes | | |
+| `ALIEN_JDL_LPMANCHORRUN` | yes | | |
+| `ALIEN_JDL_LPMPRODUCTIONTAG` | yes | | |
+| `ALIEN_JDL_LPMANCHORPRODUCTION` | yes | | |
+| `ALIEN_JDL_LPMANCHORYEAR` | yes | | |
+| `ALIEN_JDL_LPMPRODUCTIONTYPE` | yes | | Of course, that should be set to `MC`. At the moment, it is still required to be set, but it is foreseen to set this to `MC` by default and remove it from even being configurable. |
+| `ALIEN_JDL_LPMINTERACTIONTYPE` | yes | | The interaction type, choose from `pp` or `PbPb` |
+| `ALIEN_JDL_CPULIMIT` | no | 8 | The CPU limit that will be **assumed** by the workflow runner. The real limit depends on the machine it is run on. |
+| `ALIEN_JDL_SIMENGINE` | no | `TGeant4` | The engine to be used for particle transport. |
+| `ALIEN_JDL_WORKFLOWDETECTORS` | no | `ITS,TPC,TOF,FV0,FT0,FDD,MID,MFT,MCH,TRD,EMC,PHS,CPV,HMP,CTP` | This can be a subset of the detectors that were active in reconstruction. If any detector is given here that was not active in reconstruction, it will be ignored. |
+| `ALIEN_JDL_ANCHOR_SIM_OPTIONS` | no | *empty* | Any additional simulation options to allow custom user setting. See [example](#run-pythia-with-a-different-collision-system) above. |
+| `ALIEN_JDL_ADDTIMESERIESINMC` | no | `1` | Whether or not to run TPC time series. Set to `0` to disable. |
+| `SEED` | no | `${ALIEN_PROC_ID:-1}` | Set to seed the simulation. |
+| `SPLITID` | yes | | Choose the split to be simulated. See [terminology](#run-an-anchored-simulation) above. |
+| `PRODSPLIT` | yes | | Choose the maximum number of splits. See [terminology](#run-an-anchored-simulation) above. |
+| `CYCLE` | yes | | Choose the cycle within which to simulated. See [terminology](#run-an-anchored-simulation) above. |
+| `NTIMEFRAMES` | yes | | The number of timeframes to be simulated for this split. |
+| `NSIGEVENTS` | yes | | The number of signal events to be simulated per timeframe. Note that this is treated as an upper limit. The actual number of events is re-computed based in the interaction rate determined for this split. |
+
 ## Behind the scenes
 
 The procedure steered behind the scenes is quite involved. The following figure shall provide some overview.