Added equation as comment

Author: jussienko

numpy/integration/README.md

@@ -2,10 +2,18 @@
 
 A simple method for evaluating integrals numerically is by the middle Riemann sum
 
+<!--- Equation
+S = \sum_{i=1}^n f(x'_i) \Delta x
+--->
+
 ![img](http://quicklatex.com/cache3/e2/ql_30419670e67bc2b3d039e8a9d8653de2_l3.png)
 
 with
 
+<!--- Equation
+x'_i = (x_i + x_{i-1}) / 2
+--->
+
 ![img](http://quicklatex.com/cache3/09/ql_f124fd5c831e873c6abd41160fae2d09_l3.png)
 
 Use the same interval as in the first exercise and investigate how much the Riemann sum of **sin** differs from 1.0. Avoid `for` loops. Investigate also how the results changes with the choice of Δx.