Add README.md

[fiskus]

This is a finale of

• bucketFile options #2953
• Add to Package aka Shopping Cart #2955
• Open Revise Package dialog on ?action=revisePackage #2957

Addressed feedback from prev PRs:

• instead of throwing an error on the dummy context function, I just provide null as the default value
• clear method
• actions.filter → actions.every

[codecov]

Codecov Report

Merging #2960 (e1ab582) into master (8205951) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2960      +/-   ##
==========================================
- Coverage   38.95%   38.95%   -0.01%     
==========================================
  Files         615      615              
  Lines       27457    27462       +5     
  Branches     4001     4003       +2     
==========================================
  Hits        10697    10697              
- Misses      15623    15629       +6     
+ Partials     1137     1136       -1     

Flag	Coverage Δ
api-python	90.71% <ø> (ø)
catalog	12.23% <0.00%> (-0.01%)	⬇️
lambda	87.30% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
catalog/app/components/FileEditor/FileEditor.tsx	0.00% <0.00%> (ø)
catalog/app/containers/AddToPackage/Provider.tsx	0.00% <0.00%> (ø)
catalog/app/containers/Bucket/Dir.tsx	0.00% <ø> (ø)
...iners/Bucket/PackageDialog/PackageCreationForm.tsx	0.00% <0.00%> (ø)
...log/app/containers/Bucket/PackageDialog/actions.ts	0.00% <0.00%> (ø)
.../app/containers/Bucket/PackageTree/PackageTree.tsx	0.00% <ø> (ø)
catalog/app/containers/Bucket/Summary.js	0.00% <0.00%> (ø)
catalog/app/embed/Dir.js	0.00% <ø> (ø)

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[fiskus]

I removed "Add Readme" button from nested directories inside the package. We can, potentially, add Readme there too, but it needs more development and thoughts