Add a proposed anti LLM policy and move file for visibility

CONTRIBUTING.md

@@ -1,6 +1,23 @@
+
+LLM Ban Notice
+==============
+
+For various reasons, this project doesn't accept LLM code.
+Please don't submit pull requests based on generative AI
+output, and don't use AI auto completion when you write
+pull requests. If you make a pull request, please confirm
+that you've adhered to this notice or it may be closed.
+Please don't use LLMs to file issues either.
+Thank you.
+
+
+Contributions Welcome
+=====================
+
 Pull Requests and Issues are both welcome.
 
-# Responsiveness
+
+### Responsiveness
 
 General priority order is:
 
@@ -17,14 +34,16 @@ accepting them. Because I've ended up supporting a lot of libraries
 (20 as I write this, with more on the way), I am somewhat slow to
 address things. Many issues have been around for a long time.
 
-# Pull requests
+
+### Pull requests
 
 * Make sure you're using a special branch just for this pull request. (Sometimes people unknowingly use a default branch, then later update that branch, which updates the pull request with the other changes if it hasn't been merged yet.)
 * Do NOT update the version number in the file. (This just causes conflicts.)
 * Do add your name to the list of contributors. (Don't worry about the formatting.) I'll try to remember to add it if you don't, but I sometimes forget as it's an extra step.
 * Your change needs to compile as both C and C++. Pre-C99 compilers should be supported (e.g. declare at start of block)
 
-# Specific libraries
+
+### Specific libraries
 
 I generally do not want new file formats for stb_image because
 we are trying to improve its security, so increasing its attack