corrected hashlink to newsletter

faq.md

@@ -62,4 +62,5 @@ Please include the following text:
 [3]: #when-will-all-of-this-take-place
 [4]: #anything-i-can-do-to-get-things-done-faster
 [5]: #my-helmholtz-center-is-not-directly-involved-into-hifis-do-you-still-help-me
+[6]: #where-can-i-register-for-a-newsletter
 [10]: #how-should-i-acknowledge-hifis-assistance-in-a-publication