Explain how to fit FRB data.

docs/FAQ.md

@@ -2,7 +2,10 @@
 
 ## How do I fit FRB data? ##
 
-XXX
+`scatfit` reads FRB data from `SIGPROC` filterbank files and various data formats supported by `PSRCHIVE`, including PSRFITS and Timer. The data must be a single dynamic spectrum stream with frequency and time dimension, typically at zero-DM, i.e. *not* dedispersed. `scatfit` includes various methods to RFI clean the data. Thus, it can be used directly on the raw input data, assuming that you already know the rough *DM* and location of the FRB. A typical command line run looks like this:  
+`$ scatfit-fitfrb filename.fil 503.6 --fscrunch 256 --fitscatindex --snr 5.0`
+
+Tweak the sub-band *S/N* threshold as required for your data. If `scatfit` does not find the burst location automatically, you can set it manually using the *binburst* commandline option. Run `scatfit` several times while changing the input DM to the best-determined one reported in the `scatfit` output until the DM converges (no significant DM change). Use the converged best-determined DM as input for a final `scatfit` run with the large MCMC chains, i.e. without the *fast* option.
 
 ## How do I fit folded pulsar profile data? ##
 
@@ -12,7 +15,7 @@ The input data should be fully integrated in time (tscrunched) but must contain
 `$ pam -Tp -e Tp filename.fits`
 
 You can then run `scatfit` on the time and polarisation integrated data like this:  
-`$ scatfit-fitfrb filename.Tp 57.2 --fscrunch 48 --fitrange -200 200 -z -50 200 --fitscatindex --snr 3.0 --norfi`
+`$ scatfit-fitfrb filename.Tp 57.2 --fscrunch 48 --fitrange -200 200 -z -50 200 --fitscatindex --snr 15.0 --norfi`
 
 Select a good initial *DM* from the ATNF pulsar catalogue or from running `PSRCHIVE`'s `pdmp`. Use an *fscrunch* value appropriate for your data and their total number of channels. Adjust the fit and zoom range to fit our use case. The same goes for the minimum sub-band S/N. As we have cleaned the data before, we turned off all further RFI excision methods within `scatfit`.