share/mk/bsd.README: refer to the linker, not the loader

[brooks]

Summary

We're invoking the linker to create programs or libraries from one or
more object files not the loader to load them in to memory.

[emaste]

Huh this came from 4.4 Lite and has been this way for decades.

[jhb]

I fully support this in my quest for linker == static linker, or link-editor and loader == run-time loader, or dynamic linker. Certainly linker can be overloaded for both, but I only ever see loader used for loading a binary into memory, not for generating a linked executable.