minor doc repair
Summarize Racket history for v5.3.2

Merge to v5.3.2
add `file-truncate'
mach-o: handle some new load commands
mach-o: fix problems related to code signing

Strip any code signing when generating an executable from
Racket or GRacket. Also, place the __LINKEDIT segment in
virtual memory after the __PLTSCHEME segment, so that
the in-memory layout order matches the file layout order,
which in turn makes the code-signing tool's update of the
__LINKEDIT segment's size not create a virtual-memory
overlap with __PLTSCHEME.