Merge branch 'seminar-update' into 'master'

update seminar.md: add a link to Andre's talk

See merge request !14

seminar.md

@@ -53,7 +53,7 @@ and a mattermost channel for chat. To join the mattermost channel:
 |2021-02-15| - | cancelled |
 |2021-03-01| Bernhard Schröder | Framed proofs -- Linguistic aspects of proof texts and frames |
 |2021-03-15| Peter Koepke | Isabelle/Naproche |
-|2021-03-29| André Greiner-Petter | Comparative Verification of Digital Mathematical Libraries and Computer Algebra Systems |
+|2021-03-29| André Greiner-Petter | Comparative Verification of Digital Mathematical Libraries and Computer Algebra Systems ([slides](https://gist.github.com/AndreG-P/4fdbd42f313d112c888c10c2136a3620)) |
 |2021-04-12| ? | ? |
 |2021-04-26| ? | ? |
 |2021-05-10| ? | ? |