Rename "true names" to "spirits"

MarkM thinks that Vinge's version of True Names too much set the
direction of that term towards being the "unmasking" of an online
identity for a rubber hose attack

README.org

@@ -1474,7 +1474,7 @@ through argument passing.
 **** Mapping this to ActivityPub
 
 
-*** True names, public profiles, private profiles
+*** Spirits, public profiles, private profiles
 
 ** Rights amplification and group-style permissions