Add tag based convention that will prevent Roo from updating certain files based on XML tags and attributes.

[dylanturn]

Sometimes I have issues with Roo/Cline deviating from a set of instructions I gave in the form of a design spec and then updating the design document to match their changes.

I currently get around this issue by wrapping the non-negotiable parts of my documents in <INSTRUCTION immutable> </INSTRUCTION> tags. This has proven fairly effective, but updating the write_to_file tool to make sure the text it's trying to write isn't contained within a tag annotated as being immutable would be VERY helpful.