add link to information about OGC features

[ErinBecker]

The first episode includes this sentence:

The most common standard you will encounter is OGC Simple Features.

It would be useful to add a link to more information about OGC Simple Features.

[ErinBecker]

This looks like the official source: http://www.opengeospatial.org/standards/sfa, but it is quite technical and extensive. Is there a shorter bulleted list we can point learners towards to get an overview without having to wade through these 93 pages?

[obrl-soil]

Its R-specific, but SF's first vignette should work - https://cran.r-project.org/web/packages/sf/vignettes/sf1.html

[blordcastillo]

Issue looks to represent material that is no longer in any of the lessons?

[jsta]

Might still be a good idea to add a link to the sf vignette in the More Resources section:
https://github.com/datacarpentry/organization-geospatial/blob/master/_episodes_rmd/02-intro-vector-data.Rmd#L134