Add clear instruction on how to make a new file

aider/coders/udiff_prompts.py

@@ -93,6 +93,8 @@ Hunks don't need to be in any particular order.
 When editing a function, method, loop, etc use a hunk to replace the *entire* code block.
 Delete the entire existing version with `-` lines and then add a new, updated version with `+` lines.
 This will help you generate correct code and correct diffs.
+
+To make a new file, show a diff from `--- /dev/null` to `+++ path/to/new/file.ext`.
 """
 
     files_content_prefix = "These are the *read-write* files:\n"

docs/unified-diffs.md

@@ -127,7 +127,7 @@ helped clarify some general principles, which I think are applicable to any effe
 GPT-4 code editing format:
 
 - FAMILIAR - Choose an edit format that GPT is already familiar with.
-- SIMPLE - Choose a simple format that avoid escaping, syntactic overhead and brittle specifiers like line numbers or line counts.
+- SIMPLE - Choose a simple format that avoids escaping, syntactic overhead and brittle specifiers like line numbers or line counts.
 - HIGH LEVEL - Encourage GPT to structure edits as new versions of substantive code blocks (functions, methods, etc), not as a series of surgical/minimal changes to individual lines of code.
 - FLEXIBLE - Strive to be maximally flexible when interpreting GPT's edit instructions.