Add a refrence to themes_path

I had to check the source for this option

docs/10_For_Developers/Creating_a_Theme.md

@@ -71,6 +71,8 @@ Change the `theme` option inside `html`
 
 The name of the theme, is the folder name.
 
+You can use the `themes_path` setting if you want to specify a custom location of your theme folder.
+
 A variant is optional, if you want to add one, separate it from the theme with a dash.
 
 ## Overriding templates