include: document pipe path truncation behavior
include: document pipe path truncation behavior

Document the fact that the maximum path length for UNIX domain socket
paths is much less than _POSIX_PATH_MAX.

For most file systems, _POSIX_PATH_MAX is 1024 or 4096 bytes while
`sizeof(sockaddr_un.sun_path)` is typically between 92 and 108 bytes.

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso