Doc: Update Claude instructions for spell checking

CLAUDE.md

@@ -12,6 +12,7 @@
 - Avoid duplicating code in tests; when testing the same logic with different inputs, use `test.each` or shared helpers instead of repeating similar test blocks.
 - Do not make white space changes - do not add unnecessary new lines, or spaces to existing code, or wrap existing code.
 - If you add a new TypeScript file, run `yarn updateIgnored` from the root.
+- When an unknown word is detected by cSpell, handle is as per the specification in `readme/dev/spellcheck.md`
 
 ## Full Documentation