"dest" appears as optional in README but is required

[oromero]

README file shows dest parameter as optional but when not specifying it, it throws an error:

Running "htmlrefs:dist" (htmlrefs) task
Verifying property htmlrefs.dist exists in config...OK
Files: ./dist/index.html
Options: pkg={}, includes={}, buildNumber=47878
Reading ./dist/index.html...OK
Writing undefined...ERROR
Warning: Unable to write "undefined" file (Error code: undefined). Use --force to continue.

In addition to changing this in the README it would be better to actually throw the specific error, as undefined doesn't seem to be very explicit on what's wrong.