wording #2

The C++ STL is one of the most complete and reusable algorithm libraries available.
This single header file brings 80% of that functionality to C99 in a non-intrusive way.
There are no new data structures. Just include the library and call functions on C arrays.

"algorithm libraries" is unspecified and https://en.cppreference.com/w/cpp/algorithm says "The algorithms library defines functions for a variety of purposes (e.g. searching, sorting, counting, manipulating) that operate on ranges of elements. Note that a range is defined as [first, last) where last refers to the element past the last element to inspect or modify."
You might want to clarify this.

"A range of elements" here does not specify if or if not the underlying bits are continuous memory, so you might want to clarify that as well.

If you really want to stick to C++ algorithms, you could mention https://en.cppreference.com/w/c/algorithm and/or constrained algorithms.

I'd rather explain what you code does.