Document strings.Count function

Closes #1218

content/en/functions/strings.Count.md

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+---
+title: strings.Count
+description: Returns the number of non-overlapping instances of a substring within a string.
+godocref:
+date: 2020-09-07
+publishdate: 2020-09-07
+lastmod: 2020-09-07
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [count, counting, character count]
+signature: ["strings.Count SUBSTR STRING"]
+workson: []
+hugoversion:
+relatedfuncs: []
+deprecated: false
+aliases: []
+---
+
+{{< new-in "0.74.0" >}}
+
+If `SUBSTR` is an empty string, this function returns 1 plus the number of Unicode code points in `STRING`.
+
+Example|Result
+:--|:--
+`{{ "aaabaab" | strings.Count "a" }}`|5
+`{{ "aaabaab" | strings.Count "aa" }}`|2
+`{{ "aaabaab" | strings.Count "aaa" }}`|1
+`{{ "aaabaab" | strings.Count "" }}`|8