0install blog draft
Note that gcc, m4 and patch aren't currently listed as dependencies
Updates for review comments

- Note that testing your package on multiple platforms is still needed.
- Link to Windows installation of 0install. OPAM binary may come later.
- Suggest 0opam if you already have an opam command.
- Explain how 0install installs distribution packages.
- Better OPAM homepage link.
Fixed upgrade example
Use example.com in the example XML
Link to OCaml 2014 talk
Merge branch 'master' into 0install
tweak date of 0install post