Update faq.rst

[TimothyCera-NOAA]

Adding grib2io to the file format table as a way to work within xarray with GRIB2 files.

[headtr1ck]

Thanks for contributing!

While there are no strict rules about that, in the FAQ section there are only xarray internal backends. Third party libraries should instead go to the ecosystem page.

Also, feel free to add an entry in whats-new!

[TimothyCera-NOAA]

cfgrib is the default that if installed will be used, however it isn't internal to xarray. Where pygrib is neither internal nor the default and is only mentioned throughout all of xarray in the faq.rst. On the other hand I understand that you don't want every package listed here that has an xarray backend.

I will look at the ecosystem page.

[headtr1ck]

cfgrib is the default that if installed will be used, however it isn't internal to xarray.

you are right. cfgrib once was xarray internal but got deprecated because it ships with its own backend now.