Document chat account age restrictions

docs/new-account-chat-restrictions.md

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+Restricting New Accounts from Chat
+==================================
+
+With the rising availability and popularity of VPNs and proxies, dedicated
+trolls may often come back again and again with a new proxy after being IP
+banned and continue spamming.  In order to combat this, a new feature has been
+added to make it more difficult to rejoin quickly and continue spamming.
+
+Channel moderators now have the ability to configure 2 different settings:
+
+  * How long an account must be active before the user can send any chat message
+  * How long an account must be active before the user can send a chat message
+    containing a link
+
+This limit applies to both chat messages sent to the channel as well as private
+messages.  Both of these settings can be configured from the Channel Settings
+menu at the top of the page, under the General Settings tab.  By default,
+accounts must be at least 10 minutes old to chat, and 1 hour old to send links
+in chat.  Setting either restriction to 0 will disable that restriction.
+
+The age of an account is determined as follows:
+
+  * If the user is logged in as a registered account, the registration time of
+    the account is used.
+  * Otherwise, the timestamp of the session cookie is used.
+
+The session cookie is set whenever a user first joins a channel, and is reset
+whenever the user's IP address changes.  Different browsers will have different
+session cookies.