Add link to documentation

[betodealmeida]

SUMMARY

Allow users to add a link pointing to documentation.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

I added a question mark to the left of the bug nub:

ADDITIONAL INFORMATION

[ ] Has associated issue:
[X] Changes UI
[ ] Requires DB Migration. Confirm DB Migration upgrade and downgrade tested.
[X] Introduces new feature or API
[ ] Removes existing feature or API
[ ] Fixes bug
[ ] Refactors code
[ ] Adds test(s)

REVIEWERS

@mistercrunch @xtinec @khtruong @datability-io

[codecov-io]

Codecov Report

Merging #7251 into lyftga will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           lyftga    #7251      +/-   ##
==========================================
+ Coverage   64.53%   64.53%   +<.01%     
==========================================
  Files         425      425              
  Lines       20861    20862       +1     
  Branches     2280     2280              
==========================================
+ Hits        13463    13464       +1     
  Misses       7272     7272              
  Partials      126      126

Impacted Files	Coverage Δ
superset/config.py	93.78% <100%> (+0.03%)	⬆️

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[khtruong]

Can you make sure @dorq is good with these changes?

[dorq]

@betodealmeida Can you show me what the window looks like at 1680px wide?

[betodealmeida]

@dorq:

[dorq]

LGTM