State all soft dependencies after install

I finally had a time to add all of the other soft requirements. I think it makes sense to print them after installation:
```
$ gem install polisher-0.10.2.gem
======================================================
Some of the Polisher components requires the following
RubyGems and programmes to be installed:

json (RubyGem)
curb (RubyGem)
i18n (RubyGem)
pkgwat (RubyGem)
awesome_spawn (RubyGem)
gem2rpm (RubyGem)
versionomy (RubyGem)
vcr (RubyGem)
webmock (RubyGem)
git
diff
fedpkg
md5sum
koji
yum
rpmdev-packager (from rpmdevtools)
======================================================

```