Update README + docs incl. conda installation

[dominiquesydow]

Description

Update the README and docs.

Todos

• [x] Update badges in README and docs index (in sync)
• [x] Add image to docs index (in sync with README)
• [x] Update docs installation instructions (from conda; from GH)

Questions

None

Status

• [x] Ready to go

[codecov-commenter]

Codecov Report

Merging #100 (2fa2437) into master (88654c6) will increase coverage by 0.02%. The diff coverage is n/a.