add instructions to clone to install Git LFS in the repository

[zacharyburnett]

#1046 added large image files that went into Git LFS. In order to use LFS, the git hooks must be installed to the repository (git lfs install). This PR adds that step to the cloning instructions in the README.

Checklist

• added entry in CHANGES.rst under the corresponding subsection
• updated relevant tests
• updated relevant documentation
• updated relevant milestone(s)
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR

[ddavis-stsci]

I (and Nadia?) think we need to reevaluate why we need git-lsf. This is just for some small ~48K images so it seems to be overkill to me.

My error, the largest is 890K. I'm not sure we need the full resolution image for the documentation and a smaller one should be fine. We can also save space using a jpg file.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.94%. Comparing base (1a458a0) to head (df5ea63).
Report is 478 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1049   +/-   ##
=======================================
  Coverage   70.94%   70.94%           
=======================================
  Files         105      105           
  Lines        6979     6979           
=======================================
  Hits         4951     4951           
  Misses       2028     2028           

Flag	Coverage Δ		*Carryforward flag
nightly	63.06% <ø> (ø)		Carriedforward from 1a458a0

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