Added code snippet for deriving TextChatMessageProperties (#1048)

## Changes

I was trying to figure out how to derive TextChatMessageProperites, and
I couldn't find it anywhere. This PR aims to add a code snippet to the
TextChatMessageProperties page (
https://create.roblox.com/docs/reference/engine/classes/TextChatMessageProperties
) that will show how to do so.

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- [X] To the best of my knowledge, all proposed changes are accurate.

---------

Author: foshesss

content/en-us/reference/engine/classes/TextChatMessageProperties.yaml

@@ -11,6 +11,22 @@ description: |
   defined in `Class.TextChatService.OnIncomingMessage` or
   `Class.TextChannel.OnIncomingMessage`. This can be used to customize the
   appearance of a message with [rich text](../../../ui/rich-text.md) tags.
+
+  ```lua title='LocalScript - Retrieving and Using TextChatMessageProperties'
+  local TextChatService = game:GetService("TextChatService")
+  
+  TextChatService.OnIncomingMessage = function(message: TextChatMessage)
+  	-- Derive chat message properties
+  	local properties = TextChatService.ChatWindowConfiguration:DeriveNewMessageProperties()
+  
+  	-- Change color of message
+  	properties.TextColor3 = Color3.fromRGB(255, 121, 121)
+  
+  	-- Set chat window message properties
+    	message.ChatWindowMessageProperties = properties
+  
+  	return properties	
+  end
 code_samples: []
 inherits:
   - Instance