Fix markdown syntax and style for content that was moved from README.md
to docs/:
Unify the spelling of master and worker in headings and beginning of
senctences.
Also, env variable for container name in developers-guide.
Similar re-organization what was done on master branch in
a9d45c80ac.
Move all content from README.md to the Jekyll site under docs/. Also
re-organize it into multiple sub-pages.
Populate README with fresh content turning it into virtually a big link
to the html-based documentation site. Spiced up with super-quick-start
instructions.