add docs to weight function

Author: aadimator

src/NetMSA.jl

@@ -186,13 +186,13 @@ Return the weight of the row, calculated as:
 ```
 
 ```math
-w(r) =  \\begin{gather*}
-\\begin{cases}
-  w_1  \\times  \\frac{x}{c}; & \\text{ if r is not aligned}   \\
+w(r) =  \begin{gather*}
+\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{gather*}
+\end{cases}
+\end{gather*}
 ```
 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