New features: announcements WIP (#518):

* Documentation.

support/documentation/content/en/documentation/user/streamers/announcements.md

@@ -0,0 +1,31 @@
+---
+title: "Announcements"
+description: "Room owners and administrators can send special announcements in the chat."
+weight: 250
+chapter: false
+---
+
+{{% livechat_version_notice 12.0.0 %}}
+
+Room owners and administrators can send special announcements in the chat.
+
+These messages will be more visible than standard messages.
+
+To send announcements, owners and administrators will have a "{{% livechat_label announcements_message_type %}}" selector on the top of the message field:
+
+![Screenshot of a chat session. On top of the message field, there is a "{{% livechat_label announcements_message_type %}}" selector. In the chat, we can see three types of announcements: a highlighted message, an announcement, and a warning. Each of these announcements have a special color to distinguish them. The announcement and the warning have also bold titles.](/peertube-plugin-livechat/images/announcements.png?classes=shadow,border&height=400px "Announcements")
+
+There are several message types:
+
+* **{{% livechat_label announcements_message_type_standard %}}**: to send a standard message.
+* **{{% livechat_label announcements_message_type_highlight %}}**: these messages will simply be highlighted in a blue box.
+* **{{% livechat_label announcements_message_type_announcement %}}**: these messages will be in a green box, and a bold "{{% livechat_label announcements_message_type_announcement %}}" title will be added.
+* **{{% livechat_label announcements_message_type_warning %}}**: these messages will be in a rend box, and a bold "{{% livechat_label announcements_message_type_announcement %}}" title will be added.
+
+{{% notice info %}}
+User that are not owner or administrator of the chatroom can't send such messages.
+{{% /notice %}}
+
+{{% notice warning %}}
+Note: Standards XMPP clients will display announcements as standard messages.
+{{% /notice %}}