Update instructions for using leinigen profiles

[ezmiller]

I think the README instructions for working with leinigen profiles needs to be updated. I was struggling to set these up for some time, using the example in the README:

 :lein-tools-deps/config {:config-files ["foo.edn"]}
 :profiles {:dev {:lein-tools-deps/config ["bar.edn" "baz.edn"]}}

Then I finally saw the note a bit above:

Note: With lein-tools-deps 0.3.0-SNAPSHOT and earlier, the config value was a vector and looked like :tools/deps [:install :user :project], as of 0.4.0 it changed to the above map based syntax.

So I tried:

  :lein-tools-deps/config {:config-files [:install :user :project]}
  :profiles {:dev {:lein-tools-deps/config {:config-files ["dev.edn"]}}

And I think that worked, although I'm still testing.