phases: update doc to mention secret phase

mercurial/phases.py

@@ -34,6 +34,7 b' These phases share a hierarchy of traits'
             immutable shared
     public:     X        X
     draft:               X
+    secret:
 
 local commits are draft by default
 
@@ -50,6 +51,8 b' A small list of fact/rules define the ex'
 * pull never changes server states
 * publish and old server csets are seen as public by client
 
+* Any secret changeset seens in another repository is lowered to at least draft
+
 
 Here is the final table summing up the 49 possible usecase of phase exchange: