docs: Document complement

Closes https://github.com/gohugoio/hugoDocs/issues/658

docs/content/en/functions/complement.md

@@ -0,0 +1,29 @@
+---
+title: "complement"
+description: "`collections.Complement` (alias `complement`) gives the elements of a collection that are not in any of the others."
+date: 2018-11-07
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [collections,intersect,union]
+signature: ["COLLECTION | complement COLLECTION [COLLECTION]..." ]
+hugoversion: "0.51"
+aliases: []
+---
+
+Example:
+
+```go-html-template
+{{ $pages := .Site.RegularPages | first 50 }}
+{{ $news := where $pages "Type" "news" | first 5 }}
+{{ $blog := where $pages "Type" "blog" | first 5 }}
+{{ $other := $pages | complement $news $blog | first 10 }}
+```
+
+The above is an imaginary use case for the home page where you want to display different page listings in sections/boxes on different places on the page: 5 from `news`, 5 from the `blog` and then 10 of the pages not shown in the other listings, to _complement_ them.
+
+
+
+
+

docs/content/en/functions/intersect.md

@@ -10,7 +10,7 @@ categories: [functions]
 menu:
   docs:
     parent: "functions"
-keywords: []
+keywords: [collections,intersect,union,complement,symdiff]
 signature: ["intersect SET1 SET2"]
 workson: []
 hugoversion:

docs/themes/gohugoioTheme/layouts/index.html

@@ -4,7 +4,6 @@
 {{ end }}
 
 {{ define "main" }}
-
   <section class="w-100 ph4 ph5-ns pv4">
     {{- partial "home-page-sections/features-icons" . -}}
   </section>