Inclusion of new crs resource in episode 3

[taylorhixson]

In episode 03: Coordinate Reference Systems, I think a link to epsg.io in the "More Resources on CRS" box would be beneficial to learners. I'm in no way affiliated with them, but I use it frequently and find it particularly helpful when working with novice geospatial data users exploring or looking to find an appropriate crs--especially those trying to identify an unknown crs in an older static map or finding one for non-US/EU areas.