* tools/dev/unix-build/README: Mention the "nuke" target.
* tools/dev/unix-build/README: Mention the "nuke" target.

Approved by: stsp

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion