Reordered installation recommendations

[ojustino]

This is a continuation on the theme of updating the documentation. I moved AstroConda installations from most to least recommended and added a warning about expected compatibility issues with future versions of WebbPSF.

[codecov[bot]]

Codecov Report

Merging #561 (e9c446e) into develop (6d83a9d) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #561   +/-   ##
========================================
  Coverage    62.04%   62.04%           
========================================
  Files           13       13           
  Lines         5304     5304           
========================================
  Hits          3291     3291           
  Misses        2013     2013           

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