Add metaphor of open relationship

wiki/src/blueprint/explain_tails.mdwn

 [[!meta title="Explain Tails"]]
 
+Open relationship
+-----------------
+
+Tails is not my main operating system: Tails does not make me choose
+between itself and other operating systems. With Tails I have an open
+relationship. Is not my main operating system, I have other operating
+systems for other things.
+
+One in my laptop, one in my school...
+
+Tails is not jealous and does not aim to fulfill all my computer needs:
+if I need something Tails cannot give me... I can use another operating
+system!
+
+But I respect our relationship: Tails does not want to be plugged to my
+laptop if I am running other operating systems, so I never do that.
+
+And I don't use identities I use on other operating systems from the
+same Tails USB stick.
+
 <a id="iff"></a>
 
 From "[Writing good documentation](https://platform.internetfreedomfestival.org/en/IFF2018/public/schedule/custom/426)" at the IFF 2018