Update readme

[rmlarose]

Fixes #312 + the "spruce up readme" checklist todo I can't seem to find anymore.

Note I'm kinda guessing on which versions of Qiskit and pyQuil are supported. I know it works with Qiskit >= 0.19.0 and pyQuil >= 2.18.0, but earlier versions might be ok too.

[codecov]

Codecov Report

Merging #330 into master will increase coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #330      +/-   ##
==========================================
+ Coverage   91.77%   91.97%   +0.19%     
==========================================
  Files          17       17              
  Lines         827      835       +8     
==========================================
+ Hits          759      768       +9     
+ Misses         68       67       -1     

Impacted Files	Coverage Δ
mitiq/zne/scaling.py	96.53% <0.00%> (-0.34%)	⬇️
mitiq/benchmarks/utils.py	100.00% <0.00%> (ø)
mitiq/benchmarks/randomized_benchmarking.py	95.00% <0.00%> (ø)
mitiq/zne/inference.py	89.72% <0.00%> (+0.04%)	⬆️
mitiq/benchmarks/random_circuits.py	95.55% <0.00%> (+0.10%)	⬆️
mitiq/_about.py	59.25% <0.00%> (+3.25%)	⬆️
mitiq/_typing.py	100.00% <0.00%> (+18.18%)	⬆️

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[nathanshammah]

Thanks @rmlarose.
The readme is converted as rst in the documentation and then gives this page. In order for links to other (markdown) files in the repo to work also in the documentation, they need to be to the full URL link, not local, or they could point directly to the documentation version of such pages, e.g., https://mitiq.readthedocs.io/en/latest/toc_contributing.html.

[andreamari]

LGTM! I suggested two changes which should fix the linking issue mentioned by @nathanshammah .