Document zero-cost exception handling

[f0rki]

in mapping-exception-handling-to-llvm-ir/zero-cost-exception-handling.md

[LadyCailin]

Super disappointed to click on this only to see that it was empty D:

Definitely a +1 from me on this one.

For others that may want more info on this, I'll just share this link, which I have not fully grok'd yet, but I feel like probably has some good information, which, in addition to clang -S -emit-llvm, is going to be my approach to figuring this out in lieu of this article being completed.

https://monkeywritescode.blogspot.com/p/c-exceptions-under-hood.html?m=1