Updating the information on generating profiling call graph

[surbhigoel77]

Description

CONTRIBUTING.md has been updated. Information on installing the graphviz software package for successful rendering of the profiling call graph has been added. The information may help developers who are able to generate an .svg file but are not able to render the graph. Also highlighted the name of the coverage report file index.html to make it easy to locate in the reports folder (the folder contains many other html files).

Fixes #145,

Type of change

• [x] Documentation

  Key checklist

• [x] Make sure you've run the pre-commit checks: $ pre-commit run -a

• [x] All tests pass: $ poetry run pytest

Further checks

• [ ] Code is commented, particularly in hard-to-understand areas
• [ ] Tests added that prove fix is effective or that feature works

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (ad32a8e) 0.00% compared to head (dde73a8) 94.09%. Report is 2 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #147 +/- ## ============================================ + Coverage 0 94.09% +94.09% ============================================ Files 0 21 +21 Lines 0 1134 +1134 ============================================ + Hits 0 1067 +1067 - Misses 0 67 +67 ```

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[davidorme]

Looks good to me.