note about install instructions changing significantly

Author: wholmgren

docs/sphinx/source/whatsnew/v0.2.0.txt

@@ -31,6 +31,7 @@ Enhancements
 * Add optional ``projection_ratio`` keyword argument to the ``haydavies``
   calculator. Speeds calculations when irradiance changes but
   solar position remains the same (:issue:`58`)
+* Improved installation instructions in README.
 
 Bug fixes
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