Expand known issue with another workaround.

wiki/src/news/version_4.8.mdwn

@@ -76,7 +76,9 @@ For more details, read our [[!tails_gitweb debian/changelog desc="changelog"]].
   most non-english characters, including spaces ([[!tails_ticket
   17779]]). Because of this you should limit your passwords to only
   alphanumeric characters (`a-z`, `A-Z`, `0-9`) and the following
-  special characters: `_@%+=:,./-`
+  special characters: `_@%+=:,./-`. Once you have logged in you can
+  change the password however you like using the `passwd` command in a
+  Terminal.
 
 See the list of [[long-standing issues|support/known_issues]].