Fix links in README

[laurenyu]

Merge Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your pull request.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have updated the changelog with a description of my changes (if appropriate)
• I have updated any necessary documentation (if appropriate)

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

[codecov-io]

Codecov Report

Merging #218 into master will increase coverage by 0.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #218      +/-   ##
==========================================
+ Coverage   91.49%   91.74%   +0.25%     
==========================================
  Files          45       45              
  Lines        3163     3163              
==========================================
+ Hits         2894     2902       +8     
+ Misses        269      261       -8

Impacted Files	Coverage Δ
src/sagemaker/local/image.py	88.01% <0%> (+2.52%)	⬆️

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