Embedding Youtube videos

In Youtube, click 'Share→Embed' to see the values of width and height, then insert like so:

Scaling images

image scaled at 20% (click image for source site)

24021476673 d65d275d1a k

image scaled at 50% (click image for local copy on server)

24021476673 d65d275d1a k

How to embed an Asciinema recording

Including a gist

This gist might actually be useful for working on documentation: