Update dot in docs

[williamma12]

What do these changes do?

Updates docs to show that dot is now supported and does not default to modin

Related issue number

• passes flake8 modin
• passes black --check modin
• tests added and passing

[codecov]

Codecov Report

Merging #724 into master will decrease coverage by 0.22%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #724      +/-   ##
==========================================
- Coverage    90.9%   90.68%   -0.23%     
==========================================
  Files          37       37              
  Lines        6070     6074       +4     
==========================================
- Hits         5518     5508      -10     
- Misses        552      566      +14

Impacted Files	Coverage Δ
modin/engines/ray/generic/io.py	90.65% <0%> (-3.85%)	⬇️
...engines/python/pandas_on_python/frame/partition.py	93.33% <0%> (+0.22%)	⬆️
modin/engines/ray/pandas_on_ray/frame/partition.py	90.76% <0%> (+0.29%)	⬆️

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