Replace whitespace demonstrating line-breaks in GFM docs

doc/user/markdown.md

@@ -36,11 +36,15 @@ GFM honors the markdown specification in how [paragraphs and line breaks are han
 A paragraph is simply one or more consecutive lines of text, separated by one or more blank lines.
 Line-breaks, or softreturns, are rendered if you end a line with two or more spaces:
 
+[//]: # (Do *NOT* remove the two ending whitespaces in the following line.)
+[//]: # (They are needed for the Markdown text to render correctly.)
     Roses are red [followed by two or more spaces]  
     Violets are blue
 
     Sugar is sweet
 
+[//]: # (Do *NOT* remove the two ending whitespaces in the following line.)
+[//]: # (They are needed for the Markdown text to render correctly.)
 Roses are red  
 Violets are blue