add primer-marketing-utilities docs folder back

modules/primer-marketing-utilities/docs/borders.md

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+---
+title: Borders
+status: New release
+status_issue: https://github.com/github/design-systems/issues/325
+---
+
+The following border utilities are meant to used in addition to those within primer-core.
+
+{:toc}
+
+## Responsive borders
+
+Top, right, bottom, and left border utilities are can be used responsively to add or remove borders to an element at different screensizes.
+
+```html
+<div class="border-top border-sm-right border-md-bottom border-lg-top-0">
+  .border-top-0
+</div>
+```

modules/primer-marketing-utilities/docs/filters.md

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+---
+title: Filters
+status: New release
+status_issue: https://github.com/github/design-systems/issues/302
+---
+
+Filter utility classes can be applied to divs or images to apply visual effects.
+
+<div class="flash flash-warn">
+  Note: CSS filters are <a href="http://caniuse.com/#feat=css-filters">not supported by IE</a>
+</div>
+
+## Grayscale
+
+Applying `.grayscale` to an element will remove all of its colors, and make it render in black and white.
+
+```html
+<img src="<%= image_path "modules/site/home-illo-business.svg" %>" class="img-responsive grayscale" alt="">
+```