Update the editFormatInstructions configuration to specify Unified Diff format for code changes

Author: robertpiosik

packages/vscode/package.json

@@ -577,7 +577,7 @@
           "default": {
             "whole": "Whenever proposing a new or updated file, show the path in a first-line comment of a Markdown Code Block. Please show me the proposed files in full because I have a disability which means I can't type and need to be able to just copy and paste.",
             "truncated": "Whenever proposing a new or updated file, show the path in a first-line comment of a Markdown Code Block. Use ellipsis comments, e.g. \"// ...\", when appropriate.",
-            "diff": "Whenever proposing a new or updated file use the Markdown Code Block syntax. Each code block should be a diff patch."
+            "diff": "Show the changes in the Unified Diff format (compatible with git apply)."
           },
           "properties": {
             "whole": {