Add a clarification to NOTES-UNIX.md

I just wasted almost 2 hours troubleshooting, because lowercase L
and 1 look too similar, this should help some people save time.

CLA: trivial

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16295)

NOTES-UNIX.md

@@ -49,6 +49,7 @@ Notes for UNIX-like platforms
  OpenSSL's configuration scripts recognise all these options and pass
  them to the Makefile that they build. (In fact, all arguments starting
  with `-Wl,` are recognised as linker options.)
+ Please note that 'l' in '-Wl' is lowercase L and not 1.
 
  Please do not use verbatim directories in your runtime shared library
  search path!  Some OpenSSL config targets add an extra directory level