MDL-56733 boost: Add a preset repo link

theme/boost/lang/en/theme_boost.php

@@ -33,7 +33,7 @@
 $string['generalsettings'] = 'General settings';
 $string['pluginname'] = 'Boost';
 $string['presetfiles'] = 'Additional theme preset files';
-$string['presetfiles_desc'] = 'Preset files can be used to dramatically alter the appearance of the theme. See https://docs.moodle.org/dev/Boost_Presets for information on creating and sharing your own preset files.';
+$string['presetfiles_desc'] = 'Preset files can be used to dramatically alter the appearance of the theme. See <a href=https://docs.moodle.org/dev/Boost_Presets>Boost presets</a> for information on creating and sharing your own preset files, and see the <a href=http://moodle.net/boost>Presets repository</a> for presets that others have shared.';
 $string['preset'] = 'Theme preset';
 $string['preset_desc'] = 'Pick a preset to broadly change the look of the theme.';
 $string['rawscss'] = 'Raw SCSS';