Document usage of unfriendly email providers using Icedove in Tails

see https://labs.riseup.net/code/issues/11536#note-10

We need to document that “some unfriendly E-mail providers, like GMail, don’t work well in Icedove in Tails”. Gmail used OAuth, Javascript and deems that using Thunderbird is “insecure”. Furthermore their protection against connections from various places in the world sort of blocks Tor unless the user allows all this specifically and so on and so on.

Feature Branch: doc/11798-unfriendly-email-providers

Related issues

• Related to #11536 (closed)

Original created by @u on 11798 (Redmine)