feat(api): advertise talk.desec.io in welcome emails

api/desecapi/templates/emails/activate-with-domain/content.txt

@@ -1,6 +1,6 @@
 Hi there,
 
-Thank you for registering with deSEC! You are about to register the
+Thank you for registering with deSEC! You are about to set up the
 following domain: {{ domain }}
 
 To create your account and finish the registration, please confirm you
@@ -10,8 +10,14 @@ hours):
 {{ confirmation_link }}
 
 After that, please follow the instructions on the confirmation page.
-
 If link has already expired, please register again.
 
+Please also take a look at the following resources:
+
+  - Discussion forum: https://talk.desec.io/
+  - Documentation: https://desec.readthedocs.io/
+
+We hope you enjoy deSEC!
+
 Stay secure,
 Nils

api/desecapi/templates/emails/activate/content.txt

@@ -9,7 +9,14 @@ the following link (valid for {{ link_expiration_hours }} hours):
 {{ confirmation_link }}
 
 After that, please follow the instructions on the confirmation page.
-You can also find our API docs here: https://desec.readthedocs.io/
+If link has already expired, please register again.
+
+Please also take a look at the following resources:
+
+  - Discussion forum: https://talk.desec.io/
+  - Documentation: https://desec.readthedocs.io/
+
+We hope you enjoy deSEC!
 
 Stay secure,
 Nils