Update README.md

README.md

-# apipeline
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+## apipeline
+Direction-dependent calibration for Apertif. The pipeline is based on the LOFAR Default Preprocessing Pipeline (DPPP/DP3 van Diepen et al. 2018) and the wsclean imaging package (Offringa et al. 2014). It is recommended to use Docker container with the LOFAR tools installed. See the Dockerfile. 
+
+Usage: 
+```
+imcal.py [-h] [-c CONFIGFILE] [-o OUTBASE] [-s STEPS] [-f] msin
+
+DDCal Inputs
+
+positional arguments:
+  msin                  MS file to process
+
+optional arguments:
+  -h, --help            show this help message and exit
+  -c CONFIGFILE, --config CONFIGFILE
+                        Config file
+  -o OUTBASE, --outbase OUTBASE
+                        output prefix
+  -s STEPS, --steps STEPS
+                        steps to run. Example: "nvss,mask,dical,ddcal"
+  -f, --force           Overwrite the existing files
+```
+
+The config file `imcal.yml` has sections for every step with the corresponding parameters.
+Most of the parameters have explicit comments inside the config file. 
+For example the initial section *split* allows splitting the data by providing _startchan_ and _nchan_ parameters. 
+The next section, *nvss*, can be used for preliminary phase calibration against the NVSS catalog... 
+
+For more information see:
+
+`wsclean` page: https://wsclean.readthedocs.io
+
+`DPPP` page: https://support.astron.nl/LOFARImagingCookbook/dppp.html
+
+
+
+
+Citation: *Kutkin et al. 2023 (TBA)*
+