Update messaging notes with location of PGP keys

INSTALL

@@ -95,18 +95,17 @@ fi
 ./run
 
 
-Notes
-=====
 
-Messaging
+Messaging notes
+===============
 
-To replicate messages between multiple SIP devices discover PGP keys and
+To replicate messages between multiple SIP devices, discover PGP keys and
 receive messages while offline, one must install SylkServer and configure it
 with Cassandra storage backend, see https://sylkserver.com
 
 These features are compatible with other SIP clients that implement the same
 API, currently Blink for Mac and Sylk Mobile are known to support the same
-API.
+API as Blink Qt.
 
 The SIP Proxy for the account must fork a copy of all SIP messages to
 SylkServer.  When properly configured, SylkServer will respond to SIP
@@ -120,6 +119,15 @@ All settings are subsequently auto-discovered by Blink.
 To replicate messages from multiple devices they all must use the same
 private PGP key.  The import PGP panel is presented at start of messaging
 sessions for each account.  The key can be exported from another device that
-implement the same API or can be copied manually to .blink configuration
-folder.
- 
+implement the same API (see Chat menu item Export PGP private key) or can be
+copied manually to ~/.blink/keys/private configuration folder with the
+following convention:
\ No newline at end of file
+
+ * user@domain.privkey
+ * user@domain.pubkey
+
+The public keys of the recipients are looked up in SylkServer at the start
+of a messaging session.  If a key is found, it will be returned as SIP
+message with a special content type recognized by Blink and saved in a file
+e.g. ~/.blink/keys/user@domain.pubkey
+