add cautionary snippet for Continuous BehaviourSyncMode

Please warn readers that Continuous mode will send updates even when no synced variables on the script are changed. 

I spent way too long troubleshooting network performance because I assumed that Continuous mode only triggered serialization when a synced variable is changed. 

This was arguably my fault for misunderstanding Continuous mode (which, if I had to guess, is just a UDP data stream), but I assumed that Continuous mode between VRC Object Sync and UdonBehaviour were similar in that they both conditionally serialized based on changes to data.

Author: RikFlair

Tools/Docusaurus/docs/UdonSharp.md

@@ -60,7 +60,7 @@ public class Example : UdonSharpBehaviour
 | --- | --- |
 | Any | Nothing is enforced and the behaviours can be set to either sync type by the user. This is the default when no attribute is specified. |
 | None | Enforces no synced variables on the behaviour and hides the selection dropdown in the UI for the sync mode. Nothing is synced and SendCustomNetworkEvent will not work on the behaviour. |
-| Continuous | Synced variables will be updated automatically at a very frequent rate, but may not always reliably update to save bandwidth. |
+| Continuous | Synced variables will be updated automatically at a very frequent rate, but may not always reliably update to save bandwidth. Updates for synced variables will be sent even when the variable value is unchanged. |
 | Manual | Synced variables are updated manually by the user less frequently, but ensures that updates are reliable when requested. |
 | NoVariableSync | Enforces that there are no synced variables on the behaviour, hides the sync mode selection dropdown, and allows you to use the behaviours on GameObjects that use either Manual or Continuous sync. |