docs: update README

[hoffa]

Issue #, if available:

Description of changes:

Add some more correct badges, use consistent capitalization, get rid of awkward YouTube screenshot.

Description of how you validated changes:

Checklist:

• Add/update unit tests using:
  • Correct values
  • Bad/wrong values (None, empty, wrong type, length, etc.)
  • Intrinsic Functions
• Add/update integration tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Do these changes include any template validations?
  • Did the newly validated properties support intrinsics prior to adding the validations? (If unsure, please review Intrinsic Functions before proceeding).
    • Does the pull request ensure that intrinsics remain functional with the new validations?

Examples?

Please reach out in the comments, if you want to add an example. Examples will be
added to sam init through https://github.com/awslabs/aws-sam-cli-app-templates/

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #2501 (00f5cca) into develop (e7a1496) will increase coverage by 0.92%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #2501      +/-   ##
===========================================
+ Coverage    93.58%   94.50%   +0.92%     
===========================================
  Files           90       97       +7     
  Lines         6124     7301    +1177     
  Branches      1260     1523     +263     
===========================================
+ Hits          5731     6900    +1169     
- Misses         183      193      +10     
+ Partials       210      208       -2     

Impacted Files	Coverage Δ
samtranslator/region_configuration.py	77.77% <0.00%> (-22.23%)	⬇️
samtranslator/model/codedeploy.py	90.90% <0.00%> (-9.10%)	⬇️
samtranslator/validator/validator.py	91.80% <0.00%> (-3.85%)	⬇️
samtranslator/model/exceptions.py	97.67% <0.00%> (-2.33%)	⬇️
samtranslator/open_api/open_api.py	90.16% <0.00%> (-1.81%)	⬇️
samtranslator/model/s3_utils/uri_parser.py	68.42% <0.00%> (-0.81%)	⬇️
samtranslator/yaml_helper.py	89.47% <0.00%> (-0.53%)	⬇️
samtranslator/translator/logical_id_generator.py	90.62% <0.00%> (-0.29%)	⬇️
samtranslator/model/apigateway.py	96.98% <0.00%> (-0.18%)	⬇️
samtranslator/intrinsics/resource_refs.py	95.83% <0.00%> (-0.17%)	⬇️
... and 49 more

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