Add doc

README.md

@@ -48,3 +48,5 @@ def calc_routh(self):
 ```
 ```calc_routh(self)``` as the core process of this class contains initialization and process about Routh Stability Process. Firstly, it define an empty zero (basically it filled with zeros) and iteratively being inserted by ```self.den``` (refering to Routh Table principle). After that, each cell will be updated by calculating Routh Table formula 
 $$arr_{i,j} = \frac{arr_{i-1][0]*arr[i-2][j+1] - arr[i-2][0]*arr[i-1][j+1]}{arr_{i-1][0]}$$
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+This sentence uses `$` delimiters to show math inline:  $\sqrt{3x-1}+(1+x)^2$