improve readme by only leaving high-level overview and move more sections to the website with more details

[imatiach-msft]

Improve the documentation and readme website by reducing the size of the readme (and just having a general overview) and moving the sections to the website:

1.) Using interpret-community to create an explainer
2.) Local and global importance values - information about them and the APIs to compute them
3.) Raw and Engineered explanations
4.) The visualization dashboard in responsible-ai-toolbox

Note: I temporarily moved the 'latest' build in readthedocs to this branch so it would be easier to review the correctness of the changes.

[codecov-commenter]

Codecov Report

Merging #520 (d082b4f) into master (8e58580) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #520      +/-   ##
==========================================
+ Coverage   86.66%   86.70%   +0.04%     
==========================================
  Files          62       62              
  Lines        4049     4063      +14     
==========================================
+ Hits         3509     3523      +14     
  Misses        540      540              

Flag	Coverage Δ
unittests	86.70% <100.00%> (+0.04%)	⬆️

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Impacted Files	Coverage Δ
...hon/interpret_community/explanation/explanation.py	85.69% <100.00%> (+0.27%)	⬆️
python/interpret_community/lime/lime_explainer.py	95.80% <100.00%> (ø)

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