Update README.md

Update math formatting.

README.md

@@ -23,9 +23,10 @@ import cplotting_tools as cplt
 ### Examples 1 
 
 In this first set of examples the test function is the following one:
-<p align="center">
-<img src="https://render.githubusercontent.com/render/math?math=f(z)%20%3D%20%5Cfrac%7B(z%5E2-1)(z-2-i)%5E2%7D%7Bz%5E2%2B2%2B2i%7D">
-</p>
+
+$$
+f(z) = \dfrac{(z^2-1)(z-2-i)^2}{z^2+2+2i}
+$$
 
 We start defining the variables and parameters for these first examples:
 
@@ -61,9 +62,10 @@ Then, we can use the functions defined in [`cplotting_tools.py`](cplotting_tools
 ### Examples 2 
 
 In this second set of examples the test function is:
-<p align="center">
-<img src="https://render.githubusercontent.com/render/math?math=f(z)%20%3D%20%5Ccos%20z">
-</p>
+
+$$
+f(z)=\cos z
+$$
 
 As we did in the first set of examples, we start defining the variables, the parameters and the function: