Group update description (#859)

* Added groupUpdateDescription

* Updated README

Co-authored-by: Ilya Borodin <ilya.borodin@botconversa.com.br>

README.md

@@ -542,6 +542,10 @@ Of course, replace ``` xyz ``` with an actual ID.
     ``` ts
     await conn.groupUpdateSubject("abcd-xyz@g.us", "New Subject!")
     ```
+- To change the group's description
+    ``` ts
+    await conn.groupUpdateDescription("abcd-xyz@g.us", "New Description!")
+    ```
 - To change group settings
     ``` ts
     // only allow admins to send messages

src/Socket/groups.ts

@@ -100,6 +100,25 @@ export const makeGroupsSocket = (config: SocketConfig) => {
 			const participantsAffected = getBinaryNodeChildren(node!, 'participant')
 			return participantsAffected.map(p => p.attrs.jid)
 		},
+		groupUpdateDescription: async(jid: string, description?: string) => {
+			const metadata = await groupMetadata(jid);
+			const prev = metadata.descId ?? null;
+
+			await groupQuery(
+				jid,
+				'set',
+				[
+					{
+						tag: 'description',
+						attrs: {
+							...( description ? { id: generateMessageID() } : { delete: 'true' } ),
+							...(prev ? { prev } : {})
+						},
+						content: description ? [{tag: 'body', attrs: {}, content: Buffer.from(description, 'utf-8')}] : null
+					}
+				]
+			)
+		},
 		groupInviteCode: async(jid: string) => {
 			const result = await groupQuery(jid, 'get', [{ tag: 'invite', attrs: {} }])
 			const inviteNode = getBinaryNodeChild(result, 'invite')