Docs: Add help flag

docs/sections/flags.tex

@@ -8,6 +8,7 @@
     \begin{tabular}{c|c|c}
         Name & Value & Meaning \\
         \hline
+        \code{help}       & ---               & A help message that explains the \code{./tau} command. \\
         \code{view-width} & Number ($\geq 5$) & The elements of the tape that should be shown on each iteration. \\
         \code{max-iter}   & Number ($\geq 1$) & The maximum amount of iterations the Turing Machine should do.
     \end{tabular}