Update source-functions.md - Source function logging limits

Author: samkcrespo

src/connections/functions/source-functions.md

@@ -430,3 +430,7 @@ Segment alphabetizes payload fields that come in to **deployed** source function
 #### Can I use a Source Function in place of adding a Tracking Pixel to my code?
 
 No. Tracking Pixels operate client-side only and need to be loaded onto your website directly. Source Functions operate server-side only, and aren't able to capture or implement client-side tracking code. If the tool you're hoping to integrate is server-side, then you can use a Source Function to connect it to Segment. 
+
+##### What is the maximum data size that can be displayed in console.logs() when testing a Function?
+
+The test function interface has a 4KB console logging limit. Outputs surpassing this limit will not be visible in the user interface.