@trivial - update readme with clearer usage hints

[mhaack]

Description

Update readme with clearer usage hints on AEM AMS & Cloud usage

Related Issue

n/a

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have signed the Adobe Open Source CLA.
• [ ] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes and the overall coverage did not decrease.
• [ ] All unit tests pass on CircleCi.
• [ ] I ran all tests locally and they pass.

[codecov[bot]]

Codecov Report

Merging #138 into master will decrease coverage by 0.41%. The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #138      +/-   ##
============================================
- Coverage     87.77%   87.35%   -0.42%     
+ Complexity      500      495       -5     
============================================
  Files            35       35              
  Lines          1914     1914              
  Branches        299      299              
============================================
- Hits           1680     1672       -8     
- Misses           99      107       +8     
  Partials        135      135              

Flag	Coverage Δ	Complexity Δ
#integration	40.53% <ø> (-8.20%)	219.00 <ø> (-37.00)
#karma	?	?
#unittests	?	?

Impacted Files	Coverage Δ	Complexity Δ
...atalog/admin/impl/CatalogIdentifierDatasource.java	88.88% <0.00%> (-11.12%)	10.00% <0.00%> (-2.00%)
...a/impl/CatalogDataResourceProviderManagerImpl.java	78.50% <0.00%> (-2.34%)	41.00% <0.00%> (-3.00%)

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