Document release process

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Add 0.5.0 to docs

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Merge pull request #309 from orchardup/update-docs-to-be-0.5.0

Update docs to be 0.5.0