Add note to translators about text direction in browsehappy.com/public_html/functions.php

[tobifjellner]

https://meta.trac.wordpress.org/browser/sites/trunk/browsehappy.com/public_html/functions.php?marks=228#L228 contains a string that actually shouldn't be translated.

A suggestion is to add a note to translators on the row preceeding
$GLOBALS['wp_locale']->text_direction = _x( 'ltr', 'text direction', 'browsehappy' );

... something like:

/* translators: Enter the string ltr if target language is written left-to-right and rtl if target language is written right-to-left */

[coffee2code]

In 6628:

Browse Happy: Add translator comment to text direction string.

Props tobifjellner.
Fixes #3453.