Docs - Add link to videos that describe pgstac

[tylere]

Add a section for videos that describe PgSTAC. For example:

• Serving STAC Metadata with PostgreSQL using PgSTAC recorded Dec 2, 2022 at PostGIS Day 2022

[zacdezgeo]

@bitner @tylere, I wonder if we should build a more in-depth document within the docs folder that gives the textual version of the presentation. I am unsure if we want to link the presentation in the main README. My main concern is that some sections of the video content are outdated with the current state of pgSTAC. Do you have any thoughts?