Clarify LD_PRELOAD on dynamically-linked ELF
Clarify LD_PRELOAD on dynamically-linked ELF

LD_PRELOAD is an environment variable that can be set to load ELF
shared objects before all others. Linux and BSD are known to fit.
This change also unifies the use of command line, ensuring the prefix
"> " prompt.

microsoft/mimalloc,microsoft/mimalloc