Change unstable version headers

[Varunram]

Parity
  version Parity/v0.1.0-unstable-82340c0-20171222/x86_64-linux-gnu/rustc1.22.1
Copyright 2015, 2016, 2017 Parity Technologies (UK) Ltd
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.

I was on an older version of parity (v1.8.0) and wanted to upgrade versions to current master, so I pulled the repo and built the release to find the release version as 0.1.0. Now, I didn't know this was intended and proceeded to delete the repo, clean the db and rebuild only to find the same thing, when I realised that the version header was to be expected (or is it?).

I think this is highly confusing for people who build from source and comparing it to the release tag versions, most would consider it a bug. Could you include a small line in the README so that this behaviour is clearer?

[Varunram]

Looks like version 0.1.0 was defined in commit d80dd81 by PR #7136