Use github math in Readme (#107)

This makes the image render correctly in dark mode

Author: jishnub

README.md

@@ -12,7 +12,7 @@ A Julia repository for linear algebra with infinite banded and block-banded matr
 This currently supports the infinite-dimensional QR factorization for banded matrices, also known as the adaptive QR decomposition as the entries of the QR decomposition are determined lazily. 
 
 As a simple example, consider the Bessel recurrence relationship:
-<img src="https://latex.codecogs.com/svg.latex?J_{n-1}(z)-{2n\over%20z}J_n(z)+J_{n+1}(z)=0" />
+$$J_{n-1}(z)-{2n\over z}J_n(z)+J_{n+1}(z)=0$$
 This can be recast as an infinite linear system:
 ```julia
 julia> using InfiniteLinearAlgebra, InfiniteArrays, BandedMatrices, FillArrays, SpecialFunctions