Update positioning in README (#5705)

How it looks in the README:
https://github.com/PennyLaneAI/pennylane/blob/trbromley-patch-1/README.md

How it looks in the docs:
https://xanaduai-pennylane--5705.com.readthedocs.build/en/5705/

README.md

@@ -26,9 +26,11 @@
 </p>
 
 <p align="center">
-  <a href="https://pennylane.ai">PennyLane</a> is a cross-platform Python library for <a
-  href="https://en.wikipedia.org/wiki/Differentiable_programming">differentiable
-  programming</a> of quantum computers.
+  <a href="https://pennylane.ai">PennyLane</a> is a cross-platform Python library for
+  <a href="https://pennylane.ai/qml/quantum-computing/">quantum computing</a>,
+  <a href="https://pennylane.ai/qml/quantum-machine-learning/">quantum machine learning</a>,
+  and
+  <a href="https://pennylane.ai/qml/quantum-chemistry/">quantum chemistry</a>.
 </p>
 
 <p align="center">

doc/index.rst

@@ -25,9 +25,9 @@ PennyLane Documentation
 
     <div class="container mt-2 mb-2">
         <p class="lead grey-text">
-            PennyLane is a cross-platform Python library for differentiable
-            programming of quantum computers. Train a quantum computer the same
-            way as a neural network.
+          PennyLane is a cross-platform Python library for quantum computing,
+          quantum machine learning, and quantum chemistry.
+          Train a quantum computer the same way as a neural network.
         </p>
         <div class="row mt-3">