add Manel's talk to the videos

[orbeckst]

@mnmelo gave a talk on MDAnalysis at Comp Chem 2021 https://www.youtube.com/watch?v=blu2x8c6VjI

We should add it to the Video section of https://www.mdanalysis.org/pages/learning_MDAnalysis/#videos

[BhaswatiRoy]

Hello @orbeckst
The video can be added to this section with all other videos
I can work on this issue!