Add promise of Docker being stable

Docker-DCO-1.1-Signed-off-by: Timothy timothyhobbs@seznam.cz (github: https://github.com/timthelion)
I think you're not making a strong enough statement 'fundamentally' is not the same as 'stable', and the 'even before' decreases the meaning too.

perhaps we should say something more like `Docker 1.0 is the first stable release. Any major changes to existing functionality will be carefully managed using a deprecation scheme, and will only happen when absolutely needed`

clearly, we need to leave a window open for security issues...