Merge pull request #599 from bheesham/fix/doc-multi-line-comments

Add code block for multi-line comments in the docs.

manual/src/ch03-05-multicomments.md

@@ -4,8 +4,8 @@ If a comment needs to contain newlines, you may do so by having an open quote, a
 begin parsing supplied commands that are terminated. Either double or single quotes may be used
 for this purpose, depending on which quoting rules that you need.
 
+```ion
 echo "This is the first line
-this is the second line
-this is the third line"
-
-
+    this is the second line
+    this is the third line"
+```