added document on how to apply to your own gridsystem

docs/custom-grid.rst

@@ -0,0 +1,15 @@
+Using a Custom Grid
+===================
+
+Mosaic uses specific classnames which define the basic structure using rows and columns.
+The default grid system is based on Bootstrap, the default grid system from Plone 5.
+
+Integration of styles on to those classes is done by mixins in less, as you can see defined in mosaic.grid.less.
+Mixins that we use are the ones that come from mixin.grid.plone.less within the Barceloneta theme.
+
+Mosaic for now only supports full, half, thirds and quarters for the definiton, that you find in mixin.grid.plone.less.
+If you want to use your own grid system, just override the mixin classes with mixins of your choice.
+
+Pro Tip
+-------
+You problably won't want responsive styles for your edit view, because then you don't see to which position you're moving your tiles otherwise when editing on a smaller device.

docs/index.rst

@@ -14,6 +14,7 @@ The Mosaic editor lets you insert blocks (a.k.a. tiles) into the content of the
    getting-started
    content-layouts
    registry
+   custom-grid
 ..   site-layouts
 ..   typeviews