Avoid ragged option description layout

Even though the description is flush with the keys (and paragraphs), it should
be pretty clear to which key a description belongs too.

mtheme.dtx

@@ -77,7 +77,7 @@
   \begin{minipage}[t]{\textwidth}
     \textit{\textbf{\textcolor{mLightGreen}{#2}}}\dotfill\,#3\par
     \begingroup
-    \leftskip2em #4\par
+    \vspace{0.5em}#4\par
     \endgroup
   \end{minipage}
 }