add docs to weight function

Author: aadimator

src/NetMSA.jl

@@ -181,15 +181,15 @@ end
 
 Return the weight of the row, calculated as:
 
-``math
+```math
 w(r) =  \begin{equation*}
 \begin{cases}
   w_1  \times  \frac{x}{c}; & \text{ if r is not aligned}   \\
   w_2  \times  \frac{n_s}{c}; & \text{ if r is aligned}   \\
   w_3; & \text{ if r is full}   \\
 \end{cases}
 \end{equation*}
-``
+```
 where n_s is the number of occurrences of the symbol s in the aligned row r,
 and c is the total number of columns in the row. The value of x is equal to zero
 if every symbol in the row r occurred at most once, otherwise x is equal to the