Fix errors in the asciidoc ([[]] indicates a template in asciidoc)

doc/styleguide.txt

@@ -19,8 +19,8 @@ possible.  For example, do "--foo|--bar)" instead of "--@(foo|bar))".
 Rationale: the former is easier to read, often easier to grep, and
 doesn't confuse editors as bad as the latter, and is concise enough.
 
-[[ ]] vs [ ]
-------------
+[[ ]] vs [ ]
+----------------
 
 Use [[ ]] instead of [ ] when testing multiple conditions. [ ] is fine
 for single conditions where the syntax works.  Rationale: [[ ]] has
@@ -48,4 +48,5 @@ $(...) vs `...`
 
 variable and function naming
 ----------------------------
+
 /////////////////////////////////////////