Update support/known_issues for Tails 1.1

https://tails.boum.org/support/known_issues/index.en.html#index4h1 Lists issues that are no more here as of Tails 1.1rc1:

“Connect automatically” for NetworkManager connections isn’t persistent
Seems to be OK and could be safely removed (OK in my tests).

Tails could behave better when run inside VirtualBox
Seems to be also OK: #5972 (closed)

Feature Branch: doc/7590-known-issues

Parent Task: #6980 (closed)

Related issues

• Related to #5972 (closed)

Original created by @foob on 7590 (Redmine)