Add REST groups setAnnouncement docs (RocketChat#894)

Author: Marcos Spessatto Defendi

_data/toc.yml

@@ -307,6 +307,7 @@
         - removeOwner
         - rename
         - roles
+        - setAnnouncement
         - setCustomFields
         - setDescription
         - setPurpose

contributing/documentation/documentation-map/README.md

@@ -334,6 +334,7 @@ Here you can also find what articles are incomplete and missing.
             - removeOwner
             - rename
             - roles
+            - setAnnouncement
             - setCustomFields
             - setDescription
             - setPurpose

developer-guides/rest-api/README.md

@@ -128,6 +128,7 @@ When calling a production Rocket.Chat server, ensure it is running via HTTPS and
 | `/api/v1/groups.open`            | Adds the private group back to the list of groups. | [Link](groups/open/)           |
 | `/api/v1/groups.rename`          | Changes the name of the private group.             | [Link](groups/rename/)         |
 | `/api/v1/groups.roles`           | Gets the user's roles in the private group.        | [Link](groups/roles/)          |
+| `/api/v1/groups.setAnnouncement` | Sets a group's announcement.                       | [Link](groups/setannouncement/)|
 | `/api/v1/groups.setCustomFields` | Sets private group's custom fields.                | [Link](groups/setcustomfields/)|
 | `/api/v1/groups.setDescription`  | Sets a private group's description.                | [Link](groups/setdescription/) |
 | `/api/v1/groups.setPurpose`      | Sets a private group's description.                | [Link](groups/setpurpose/)     |

developer-guides/rest-api/groups/README.md

@@ -25,6 +25,7 @@
 | `/api/v1/groups.removeOwner` | Removes the role of owner from a user in a group. | [Link](removeowner/) |
 | `/api/v1/groups.rename` | Changes the name of the private group. | [Link](rename/) |
 | `/api/v1/groups.roles` | Gets the user's roles in the private group. | [Link](roles/) |
+| `/api/v1/groups.setAnnouncement` | Sets a group's announcement. | [Link](setannouncement/)|
 | `/api/v1/groups.setCustomFields` | Sets private group's custom fields. | [Link](setcustomfields/) |
 | `/api/v1/groups.setDescription` | Sets a private group's description. | [Link](setdescription/) |
 | `/api/v1/groups.setPurpose` | Sets a private group's description. | [Link](setpurpose/) |

developer-guides/rest-api/groups/setannouncement/README.md

@@ -0,0 +1,39 @@
+# Group Set Announcement
+
+Sets the announcement for the group.
+
+| URL | Requires Auth | HTTP Method |
+| :--- | :--- | :--- |
+| `/api/v1/groups.setAnnouncement` | `yes` | `POST` |
+
+## Payload
+
+| Argument | Example | Required | Announcement |
+| :--- | :--- | :--- | :--- |
+| `roomId` | `ByehQjC44FwMeiLbX` | Required | The group's id |
+| `announcement` | `Test out everything.` | Required | The announcement to set for the group. |
+
+## Example Call
+
+```bash
+curl -H "X-Auth-Token: 9HqLlyZOugoStsXCUfD_0YdwnNnunAJF8V47U3QHXSq" \
+     -H "X-User-Id: aobEdbYhXfu5hkeqG" \
+     -H "Content-type: application/json" \
+     http://localhost:3000/api/v1/groups.setAnnouncement \
+     -d '{ "roomId": "ByehQjC44FwMeiLbX", "announcement": "Test out everything" }'
+```
+
+## Example Result
+
+```json
+{
+  "announcement": "Test out everything.",
+  "success": true
+}
+```
+
+## Change Log
+
+| Version | Description |
+| :--- | :--- |
+| 0.70.0 | Added |