add pgp key

people/jbetzendahl.md

@@ -20,4 +20,4 @@ My Bachelor Thesis at Bielefeld University had the topic of implementing Inverse
 
 I'm interested in logic, theorem proving, category theory, type theory and (formal) mathematics.
 
-If you want to contact me, my email address is _myFirstName_._myLastName_@fau.de
+If you want to contact me, my email address is _myFirstName_._myLastName_@fau.de (public pgp-key is [here](keys/0xC64D686FC97D4B2D.asc))