[docs] Fix CORS section in installation

[graceguo-supercat]

CATEGORY

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• Bug Fix
• Enhancement (new features, refinement)
• Refactor
• Add tests
• Build / Development Environment
• Documentation

SUMMARY

Fix the extra CORS Dependency in Superset installation step.

TEST PLAN

https://superset.incubator.apache.org/installation.html#cors

ADDITIONAL INFORMATION

REVIEWERS

@michellethomas @mistercrunch @etr2460

[codecov-io]

Codecov Report

Merging #8958 into master will decrease coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #8958     +/-   ##
=========================================
- Coverage   58.97%   58.68%   -0.3%     
=========================================
  Files         359      362      +3     
  Lines       11333    11415     +82     
  Branches     2787     2801     +14     
=========================================
+ Hits         6684     6699     +15     
- Misses       4471     4538     +67     
  Partials      178      178

Impacted Files	Coverage Δ
...t/assets/src/dashboard/reducers/dashboardLayout.js	93% <0%> (-1.9%)	⬇️
...et/assets/src/dashboard/actions/dashboardLayout.js	95.09% <0%> (-1.88%)	⬇️
...uperset/assets/src/dashboard/components/Header.jsx	41.46% <0%> (-1.78%)	⬇️
...ssets/src/dashboard/containers/DashboardHeader.jsx	100% <0%> (ø)	⬆️
...src/dashboard/components/HeaderActionsDropdown.jsx	69.56% <0%> (ø)	⬆️
superset/assets/src/dashboard/reducers/index.js	100% <0%> (ø)	⬆️
...set/assets/src/dashboard/reducers/dashboardInfo.js	66.66% <0%> (ø)
...rset/assets/src/dashboard/actions/dashboardInfo.js	33.33% <0%> (ø)
...ssets/src/dashboard/components/PropertiesModal.jsx	7.4% <0%> (ø)
...src/dashboard/util/getFilterConfigsFromFormdata.js	88.46% <0%> (+1.5%)	⬆️

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[etr2460]

doc change seems fine. I'm a bit confused why you'd need to separately install another dep instead of it being included in requirements or requirements-extra, but i don't have the historical context

[graceguo-supercat]

CORS is optional for Superset app. it's contributed by community:
#478
I guess most of users/companies don't need to handle cross-domain issue.

[villebro]

What is the purpose of this change? If the purpose is to describe the process when not installing Superset via pip, then I think it might be better to explain when this alternative approach is needed.

[graceguo-supercat]

I feel confused by the current instruction. I am ok with all options .

Before:

After:

[mistercrunch]

It's slightly better to recommend pip install apache-superset[cors], that way it will reference the version range or pinned version specified in setup.py

[graceguo-supercat]

Updated.