Fix formatting in PyTorch README and remove SDK version in general README

[laurenyu]

Issue #, if available:
Just some minor things I noticed while reading the READMEs. Also, figured we should remove the explicit SDK version reference because it's so easy for that to become outdated.

Description of changes:

Merge Checklist

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• I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[codecov-io]

Codecov Report

Merging #363 into master will decrease coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #363      +/-   ##
=========================================
- Coverage   93.07%   92.9%   -0.17%     
=========================================
  Files          51      51              
  Lines        3567    3567              
=========================================
- Hits         3320    3314       -6     
- Misses        247     253       +6

Impacted Files	Coverage Δ
src/sagemaker/local/image.py	87.38% <0%> (-1.81%)	⬇️

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