DOC: Add Codecov badge to README

[fepegar]

It looks like this:

[codecov-commenter]

Codecov Report

Merging #343 (792be72) into main (7ddb45d) will increase coverage by 4.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #343      +/-   ##
==========================================
+ Coverage   76.74%   80.85%   +4.11%     
==========================================
  Files          64       28      -36     
  Lines        5629     2382    -3247     
  Branches      895      352     -543     
==========================================
- Hits         4320     1926    -2394     
+ Misses       1117      354     -763     
+ Partials      192      102      -90     

Impacted Files	Coverage Δ
hi-ml-azure/src/health_azure/himl_tensorboard.py
...stopathology/src/histopathology/utils/wsi_utils.py
...opathology/src/histopathology/models/transforms.py
...ology/src/histopathology/datasets/panda_dataset.py
hi-ml-azure/src/health_azure/himl_download.py
...src/histopathology/datasets/panda_tiles_dataset.py
...opathology/src/histopathology/utils/layer_utils.py
hi-ml-azure/src/health_azure/traverse.py
...histopathology/datasets/tcga_crck_tiles_dataset.py
hi-ml-azure/src/health_azure/datasets.py
... and 26 more

---

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[fepegar]

@ant0nsc do you know why Codecov might be reporting a large difference in coverage for this? Also, why is coverage uploaded twice in the build workflow? I missed that in the PR.

hi-ml/.github/workflows/build-test-pr.yml

Lines 207 to 211 in 7ddb45d

	- name: Upload coverage report to Codecov
	if: ${{ matrix.packageName == '*.whl' }}
	uses: codecov/codecov-action@v2
	with:
	name: ${{ matrix.folder }}

hi-ml/.github/workflows/build-test-pr.yml

Lines 262 to 266 in 7ddb45d

	- name: Upload coverage report to Codecov
	if: ${{ matrix.packageName == '*.whl' }}
	uses: codecov/codecov-action@v2
	with:
	name: ${{ matrix.folder }}

[fepegar]

Apparently, the difference shown here might have been "a timing issue".

[ant0nsc]

@fepegar , Uploading is happening twice because first we do it for hi-ml and hi-ml-azure (matrix), and then in line 262 for the histo folder. However... For this run, there is no sign of results from hi-ml-azure? (screenshot from https://app.codecov.io/gh/microsoft/hi-ml/compare/343/tree)

Previous run correctly had numbers also for hi-ml-azure.

[fepegar]

Thanks for clarifying. No idea why that happened! It looks ok for more recent commits.