Issue 8307 and 13336 - fix documentation around return type inference and ref deduction

[Issue 8307](https://issues.dlang.org/show_bug.cgi?id=8307) - inconsistent treatment of auto functions
[Issue 13336](https://issues.dlang.org/show_bug.cgi?id=13336) - auto ref return deduced to be ref despite return value coercion
What could that paragraph possibly mean?
It was added with https://github.com/D-Programming-Language/dlang.org/commit/d0a87f813fc684dcea499738f2583bca3d2ce3ac.