Update 'Chatrooms' in 17.md

Specifies updated conventions for Direct Message Chatrooms in  NIP-17.  

addresses issue nostr-protocol#1297 

implemented in recent [PR for NDK](nostr-dev-kit/ndk#327)

Author: manimejia

17.md

@@ -82,13 +82,15 @@ Kind `15` is used for sending encrypted file event messages:
 
 Just like kind `14`, kind `15`s MUST never be signed.
 
-## Chat Rooms
+## Threads and Chatrooms
 
-The set of `pubkey` + `p` tags defines a chat room. If a new `p` tag is added or a current one is removed, a new room is created with a clean message history.
+Without formally specifying an event kind for chatroom config, the following are conventions for achieving consistent direct message user experiences across clients. 
 
-Clients SHOULD render messages of the same room in a continuous thread.
+Clients SHOULD organize message events into 'threads'. A 'thread' SHOULD be a set of message events with a matching set of 'member' pubkeys (`pubkey` field + `p` tag values). Clients receiving or creating a message event with one or more different 'members' (from an existing 'thread') SHOULD add this message in a new thread with a clean message history.
 
-An optional `subject` tag defines the current name/topic of the conversation. Any member can change the topic by simply submitting a new `subject` to an existing `pubkey` + `p` tags room. There is no need to send `subject` in every message. The newest `subject` in the chat room is the subject of the conversation.
+Clients MAY render one or more 'threads' as a 'chatroom'. Clients SHOULD render all messages of a single 'thread' in a single 'chatroom'. In the case of multiple 'threads' in a single 'chatroom', clients SHOULD indicate the 'members' alongside each message rendered in a 'chatroom', and clients SHOULD provide a means for selecting desired 'members' when authoring new messages.
+
+A 'chatroom' MAY have a name or topic set (privately) by the end user OR for all 'thread members' by any message. The optional `subject` tag of any message events MAY be used to set the default name or topic of a 'chatroom'. In this case, the most recent message with a `subject` tag, in the set of 'chatroom threads', SHOULD be used to set the name or topic of the 'chatroom'.
 
 ## Encrypting