Update part3b.md

I have heard some people trying to deploy their FullStackOpen repos as a whole for their backend for Phonebook, so adding a little note that tells them to have a separate github repo might remedy future errors while deploying their backend.

Author: FurkanCodes

src/content/3/en/part3b.md

@@ -399,6 +399,8 @@ Note that the directory paths in the script <i>build:ui</i> depend on the locati
 
 #### Render
 
+Note: When you attempt to deploy your backend to Render, make sure you have a seperate repository for the backend and deploy that github repo through Render, attempting to deploy through your Fullstackopen repository will often throw "ERR path ....package.json". 
+
 In case of Render, the scripts look like the following
 
 ```json