Update style-guidelines.adoc

fixing the headers

Signed-off-by: Kersten Richter <kersten@riscv.org>

src/style-guidelines.adoc

@@ -3,7 +3,7 @@
 
 All professional technical writers eventually learn to keep their writing as simple as possible.
 
-== Avoid statements that will soon be out of date
+=== Avoid statements that will soon be out of date
 
 Avoid words like "currently" and "new." A feature that is new today might not be considered new in a few months.
 
@@ -20,7 +20,7 @@ Avoid words like "currently" and "new." A feature that is new today might not be
 |===
 
 
-== Avoid words that assume a specific level of understanding
+=== Avoid words that assume a specific level of understanding
 
 
 Avoid words such as "just", "simply", "easy", "easily", or "simple". These words do not add value.