Add comment about trailing whitespace in Markdown

Related to #88 (Github Pull Request)

.editorconfig

@@ -20,5 +20,8 @@ indent_style = space
 indent_size = 2
 
 # Markdown Files
+#
+# Two spaces at the end of a line in Markdown mean "new line",
+# so trimming trailing whitespace for such files can cause breakage.
 [*.md]
 trim_trailing_whitespace = false