Added k4run documentation

README.md

@@ -1,8 +1,10 @@
 # k4FWCore (key4hep FrameWork Core)
 
-k4FWCore is a Gaudi package that provides the PodioDataService, that allows to
+k4FWCore is a Gaudi package that provides the PodioDataService, which allows to
 use podio-based event data models like EDM4hep in Gaudi workflows.
 
+k4FWCore also provides the `k4run` script used to run Gaudi steering files.
+
 ## Components
 
 ### Basic I/O
@@ -13,12 +15,38 @@ Component wrapping the PodioDataService to handle PODIO types and collections.
 
 #### PodioInput
 
-Algorithm to read data from input file(s) on disk.
+Algorithm to read data from one or multiple input file(s) on disk.
 
 #### PodioOutput
 
-Algorithm to write data to output file on disk.
+Algorithm to write data to an output file on disk.
+
+## k4run
+```bash
+$ k4run --help
+usage: k4run [-h] [--dry-run] [-v] [-n NUM_EVENTS] [-l] [--gdb] [--ncpus NCPUS] [config_files ...]
+
+Run job in the Key4HEP framework
 
+positional arguments:
+  config_files          Gaudi config (python) files describing the job
+
+options:
+  -h, --help            show this help message and exit
+  --dry-run             Do not actually run the job, just parse the config files
+  -v, --verbose         Run job with verbose output
+  -n NUM_EVENTS, --num-events NUM_EVENTS
+                        Number of events to run
+  -l, --list            Print all the configurable components available in the framework and exit
+  --gdb                 Attach gdb debugger
+  --ncpus NCPUS         Start Gaudi in parallel mode using NCPUS processes. 0 => serial mode (default), -1 => use all CPUs
+```
+When supplied with a Gaudi steering file `k4run --help file.py` also shows the settable properties of the Gaudi algorithms used in the file. Additionally, it is possible to add further arguments and use them in the steering file by using the python `argparse.ArgumentParser` shared by `k4run`.
+```python
+parser.add_argument("-f", "--foo", type=int, help="hello world")
+my_opts = parser.parse_known_args()
+print(my_opts[0].foo)
+```
 
 ## Dependencies
 
@@ -30,7 +58,7 @@ Algorithm to write data to output file on disk.
 
 ## Installation and downstream usage.
 
-k4FWCore is a cmake project. After setting up the dependencies (use for example `source /cvmfs/sw.hsf.org/key4hep/setup.sh`)
+k4FWCore is a CMake project. After setting up the dependencies (use for example `source /cvmfs/sw.hsf.org/key4hep/setup.sh`)
 
 
 ```