add paragraph spacing instruction to README

README.md

@@ -19,9 +19,10 @@ It provides visual accessibility improvements.
 ### Note
 * IE11 cannot apply filters. This means that images and videos will not be transformed in IE11.
 * All colour transformations are applied by mathematical shifts. It is therefore important that the course start from AA colour contrast for the algorithms to be applicable.
+* Invert only inverts brightness, not colour.
 * Line height, paragraph spacing, letter spacing and word spacing are all ratio based. 1 is the current value, 1.2 is and uplift by 20%, 0.9 would be a shift downwards by 10%.
+* In order to support paragraph spacing, all body text needs to be wrapped in [paragraph tags](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/p).
 * Font size medium is the default font size (16px usually), large is 18pt, small is 9pt.
-* Invert only inverts brightness, not colour.
 * Hide decorative images is contingent on alt text.
 
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