Update whitespace readme

Add note about not making unnecessary affordances for Windows line endings.

Author: Timmmm

lints/lint_whitespace/README.md

@@ -1,3 +1,7 @@
 # Whitespace Lint
 
 This lint trims trailing whitespace and ensures there is exactly one newline at the end of files. It also ensures Unix file endings.
+
+The default filter matches all text files (no 0 byte in the first 8000 bytes). It does not have special handling for Windows line endings (CRLF) - they will be modified to be LF. All text editors on Windows support Unix line endings (LF), so I recommend just switching your editors to use that, and configuring Git to fix them on commit like this:
+
+    git config --global core.autocrlf input