Mention cleanupListOfValues in README (see svg#287)

README.md

@@ -44,6 +44,7 @@ Today we have:
 * [ [ removeUnusedNS](https://github.com/svg/svgo/blob/master/plugins/removeUnusedNS.js) ] remove unused namespaces declaration
 * [ [ cleanupIDs](https://github.com/svg/svgo/blob/master/plugins/cleanupIDs.js) ] remove unused and minify used IDs
 * [ [ cleanupNumericValues](https://github.com/svg/svgo/blob/master/plugins/cleanupNumericValues.js) ] round numeric values to the fixed precision, remove default 'px' units
+* [ [ cleanupListOfValues](https://github.com/svg/svgo/blob/master/plugins/cleanupListOfValues.js) ] round numeric values in attributes that take a list of numbers, like viewport or enableBackground
 * [ [ moveElemsAttrsToGroup](https://github.com/svg/svgo/blob/master/plugins/moveElemsAttrsToGroup.js) ] move elements attributes to the existing group wrapper
 * [ [ moveGroupAttrsToElems](https://github.com/svg/svgo/blob/master/plugins/moveGroupAttrsToElems.js) ] move some group attributes to the content elements
 * [ [ collapseGroups](https://github.com/svg/svgo/blob/master/plugins/collapseGroups.js) ] collapse useless groups