- Fix link to client repo (it's DMDirc/DMDirc not DMDirc/client)
- Add shiny screenshot
- Add information on actually installing and running

The "Run DMDirc" configuration will run DMDirc with the profile
dir set to etc/profile, which is set up with a symlink to
the latest plugins.

For now, copy the defaults and mode aliases there too, as the
dev client won't extract them.

Will move the PMD tasks/config to meta at some point.

This reverts commit 7ec738a776.