docs: add comment explaining check for escaped percent sign

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---

Author: anandkaranubc

lib/node_modules/@stdlib/string/base/format-tokenize/lib/main.js

@@ -73,6 +73,7 @@ function formatTokenize( str ) {
 		if ( content.length ) {
 			tokens.push( content );
 		}
+		// Check for an escaped percent sign %%...
 		if ( match[ 6 ] === '%' ) {
 			tokens.push( '%' );
 		} else {