Documentation for get_fisher_matrix

[elisachisari]

Doc strings needed for the function get_fisher_matrix:

augur/augur/analyze.py

Line 494 in 1cbcb12

def get_fisher_matrix(self, method='5pt_stencil', save_txt=True):

[fjaviersanchez]

Is it okay to close this by #110, @elisachisari?