Fix markdown for code sample

Author: SamuelMarks

README.rst

@@ -258,11 +258,12 @@ The following actions are available out of the box. They may be used in either
     may be used.
 
 ``StoreOption``
-    As ``Store``, but wrap value with ``Some`` for use with ``Option``. For
-    example:
+    As ``Store``, but wrap value with ``Some`` for use with ``Option``. For example:
 
-        let mut x: Option<i32> = None;
-        ap.refer(&mut x).add_option(&["-x"], StoreOption, "Set var x");
+```Rust
+let mut x: Option<i32> = None;
+ap.refer(&mut x).add_option(&["-x"], StoreOption, "Set var x");
+```
 
 ``StoreConst(value)``
     An option has no arguments. Store a hard-coded ``value`` into variable,