Description under Friends

See: https://www.boost.org/doc/libs/1_74_0/libs/beast/doc/html/beast/ref/boost__beast__multi_buffer.html

Produced from this file:

https://github.com/boostorg/beast/blob/4fbb0079c34e1e42e6d7527fd927163b3d2413de/include/boost/beast/core/multi_buffer.hpp

Note that the error seems only to manifest in the documentation of the typedef `issue_50`, not the template to which it refers: `basic_issue_50<>`