Document specific detector setup for TRK

Added specific detector setup details and configurables for TRK detector.

Author: njacazio

Detectors/Upgrades/ALICE3/TRK/README.md

@@ -6,5 +6,23 @@
 
 This is top page for the TRK detector documentation.
 
+
+## Specific detector setup
+
+
+Configurables for various sub-detectors are presented in the following Table:
+
+| Subsystem          | Available options                                       | Comments                                                         |
+| ------------------ | ------------------------------------------------------- | ---------------------------------------------------------------- |
+| `TRKBase.layoutVD` | `kIRIS4` (default), `kIRISFullCyl`, `kIRIS5`, `kIRIS4a` | [link to definitions](./base/include/TRKBase/TRKBaseParam.h) |
+| `TRKBase.layoutML` | `kCylinder`, `kTurboStaves` (default), `kStaggered`     |                                                                  |
+| `TRKBase.layoutOT` | `kCylinder`, `kTurboStaves`, `kStaggered` (default)     |                                                                  |
+
+For example, a geometry with fully cylindrical tracker barrel (for all layers in VD, ML and OT) can be obtained by
+```bash
+o2-sim-serial-run5 -n 1 -g pythia8hi -m A3IP TRK FT3 TF3 \
+  --configKeyValues "TRKBase.layoutVD=kIRISFullCyl;TRKBase.layoutML=kCylinder;TRKBase.layoutOL=kCylinder"
+```
+
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