updated the link with markdown link syntax

updated the link in the comment so it helps with generated docs

src/options/vars.rs

@@ -16,7 +16,7 @@ pub static COLUMNS: &str = "COLUMNS";
 pub static TIME_STYLE: &str = "TIME_STYLE";
 
 /// Environment variable used to disable colors.
-/// See: https://no-color.org/
+/// See: <https://no-color.org/>
 pub static NO_COLOR: &str = "NO_COLOR";
 
 // exa-specific variables