added version pin to install instructions

[shimwell]

Adds versions to the install instructions

[codecov]

Codecov Report

Merging #245 (297a76b) into main (798d7f5) will decrease coverage by 0.52%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #245      +/-   ##
==========================================
- Coverage   95.29%   94.77%   -0.53%     
==========================================
  Files          82       82              
  Lines        5507     5507              
==========================================
- Hits         5248     5219      -29     
- Misses        259      288      +29     

Impacted Files	Coverage Δ
paramak/reactor.py	69.01% <0.00%> (-3.93%)	⬇️
paramak/utils.py	83.80% <0.00%> (-2.28%)	⬇️
paramak/shape.py	93.27% <0.00%> (-1.90%)	⬇️

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