Merge #540

540: Update list of similar units implementations r=hgrecco

I added astropy.units and yt, as those were missing from the list.

Speaking of which, has there been any talk of maybe combining some of these packages? It feels a bit like the number of these is growing exponentially.

docs/faq.rst

@@ -35,4 +35,9 @@ You mention other similar Python libraries. Can you point me to those?
 
 `cf units <https://github.com/SciTools/cf_units>`_
 
+`astropy units <https://github.com/astropy/astropy>`_
+
+`yt <https://github.com/yt-project/yt>`_
+
+
 If your are aware of another one, please contribute a patch to the docs.