couple of cosmetic fixes to docs

[vishal-ph]

Description

Quick changes to documentation organization:

• RQAOA workflows is part of workflows section
• Changes in organization of backends and devices

[codecov]

Codecov Report

Merging #128 (6276e6a) into dev (80b0b6b) will increase coverage by 0.00%.
The diff coverage is 27.41%.

@@           Coverage Diff           @@
##              dev     #128   +/-   ##
=======================================
  Coverage   87.30%   87.30%           
=======================================
  Files          67       67           
  Lines        8924     8928    +4     
=======================================
+ Hits         7791     7795    +4     
  Misses       1133     1133           

Impacted Files	Coverage Δ
openqaoa/backends/qpus/qaoa_braket_qpu.py	21.59% <0.00%> (-0.51%)	⬇️
tests/test_qpu_braket.py	10.38% <6.97%> (-0.44%)	⬇️
openqaoa/devices.py	50.00% <33.33%> (+1.42%)	⬆️
openqaoa/workflows/optimizer.py	89.69% <100.00%> (ø)
tests/test_workflows.py	100.00% <100.00%> (ø)
openqaoa/optimizers/result.py	90.69% <0.00%> (-1.17%)	⬇️

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