DOC: Clarify Gravitation Waves caption

It's dramatic and I struggled with changing it, but the
original wording makes NumPy rather than gravitational waves
the antecedent of "they".

Author: bjnath

config.yaml

@@ -45,7 +45,7 @@ params:
       alttext: First image of a black hole. It is an orange circle in a black background.
       url: /case-studies/blackhole-image
     - title: Detection of Gravitational Waves
-      text: One hundred years after they were predicted by Albert Einstein, NumPy was instrumental in the first observation of gravitational waves by LIGO in 2016.
+      text: In 1916, Albert Einstein predicted gravitational waves; 100 years later their existence was confirmed by LIGO scientists using NumPy.
       img: images/content_images/case_studies/gravitional.png
       alttext: Two orbs orbiting each other. They are displacing gravity around them.
       url: /case-studies/gw-discov