updating docs

[scarrazza]

Fixes some docs issues and include conda instructions.

[codecov]

Codecov Report

Merging #493 (3b4f2ae) into master (e82bc3e) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #493   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           85        85           
  Lines        12084     12084           
=========================================
  Hits         12084     12084           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e82bc3e...3b4f2ae. Read the comment docs.

[mlazzarin]

Looks good to me.

[andrea-pasquale]

Looks good to me as well.

[stavros11]

Looks good to me too, we should only update the Qiskit version in the benchmarks table according to the qibo paper.