Update default town square purpose (#5810)

webapp/i18n/en.json

@@ -1227,6 +1227,7 @@
   "custom_emoji.empty": "No custom emoji found",
   "custom_emoji.header": "Custom Emoji",
   "custom_emoji.search": "Search Custom Emoji",
+  "default_channel.purpose": "Post messages here that you want everyone to see. Everyone automatically becomes a permanent member of this channel when they join the team.",
   "delete_channel.cancel": "Cancel",
   "delete_channel.channel": "channel",
   "delete_channel.confirm": "Confirm DELETE Channel",
@@ -1528,7 +1529,7 @@
   "intro_messages.beginning": "Beginning of {name}",
   "intro_messages.channel": "channel",
   "intro_messages.creator": "This is the start of the {name} {type}, created by {creator} on {date}.",
-  "intro_messages.default": "<h4 class='channel-intro__title'>Beginning of {display_name}</h4><p class='channel-intro__content'><strong>Welcome to {display_name}!</strong><br/><br/>This is the first channel teammates see when they sign up - use it for posting updates everyone needs to know.</p>",
+  "intro_messages.default": "<h4 class='channel-intro__title'>Beginning of {display_name}</h4><p class='channel-intro__content'><strong>Welcome to {display_name}!</strong><br/><br/>Post messages here that you want everyone to see. Everyone automatically becomes a permanent member of this channel when they join the team.</p>",
   "intro_messages.group": "private group",
   "intro_messages.invite": "Invite others to this {type}",
   "intro_messages.inviteOthers": "Invite others to this team",