[BoundsSafety] BoundsSafety.html fails to document __unsafe_null_terminated_from_indexable et al

[seanm]

Playing with -fbounds-safety I got a compiler error than included the text:

Consider using '__unsafe_null_terminated_from_indexable()' to perform this conversion. Note this performs a linear scan of memory to find the null terminator

So I went to read more about it at:

https://clang.llvm.org/docs/BoundsSafety.html

But the string null_terminated_from does not appear in that document at all. It should.