Add a math label and equation link link

Author: Blendify

demo_docs/source/index.rst

@@ -41,13 +41,16 @@ This is a test. Here is an equation:
 Here is another:
 
 .. math::
+    :label: This is a label
 
     \nabla^2 f =
     \frac{1}{r^2} \frac{\partial}{\partial r}
     \left( r^2 \frac{\partial f}{\partial r} \right) +
     \frac{1}{r^2 \sin \theta} \frac{\partial f}{\partial \theta}
     \left( \sin \theta \, \frac{\partial f}{\partial \theta} \right) +
     \frac{1}{r^2 \sin^2\theta} \frac{\partial^2 f}{\partial \phi^2}
+    
+You can add a link to equations like the one above :eq:`This is a label` by using ``:eq:``.
 
 Tables
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