Add linear model Jupyter Notebook

[teubert]

Add linear model jupyter notebook developed by @aqitya and approved here: nasa/prog_models#551 (review)

The only changes from this approved PR are:

1. Removed old linear model example (that this replaces), and
2. changed prog_models -> progpy in import

[github-actions]

Thank you for opening this PR. Each PR into dev requires a code review. For the code review, look at the following:

• Reviewer (someone other than author) should look for bugs, efficiency, readability, testing, and coverage in examples (if relevant).
• Ensure that each PR adding a new feature should include a test verifying that feature.
• All errors from static analysis must be resolved.
• Review the test coverage reports (if there is a change) - will be added as comment on PR if there is a change
• Review the software benchmarking results (if there is a change) - will be added as comment on PR
• Any added dependencies are included in requirements.txt, setup.py, and dev_guide.rst (this document)
• All warnings from static analysis must be reviewed and resolved - if deemed appropriate.

[codecov-commenter]

Codecov Report

Merging #70 (2b78b18) into dev (1485c8a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev      #70   +/-   ##
=======================================
  Coverage   84.19%   84.19%           
=======================================
  Files          99       99           
  Lines       10111    10111           
=======================================
  Hits         8513     8513           
  Misses       1598     1598           

[aqitya]

Pushed some changes to how we were directing users to ProgPy documentation.

[teubert]

I reviewed @Aqity's pushed changed and approve