Update BuildStream's documentation and website with an update on the Release Policy change

Background

From #901 (closed); basically:

• 1.2.x will not be actively maintained long term
• new version will be 2.0 which will break api

Task description

• Update website - website!118 (merged)
• Update README
• Blog post - https://blogs.gnome.org/tvb/2019/03/04/buildstream-news-and-2-0-planning/

Acceptance Criteria

All is updated

changed the description

Updated description with link to blog post

changed the description

webiste update in progress, added link to the description website!118 (merged)

Having read the README, not sure this really needs updating

marked the checklist item Update website - website!118 (merged) as completed

changed the description

marked the checklist item Update README as completed

marked the checklist item Update README as incomplete

closing this now that the website has been updated with a news story:

https://buildstream.build/articles/2019/buildstream-news-and-2.0-planning/

@jjardon any other places we'll need to update? Maybe there is someone or a group of people specifically at GNOME we should ping?

closed