chore(markdown): Updated utils docs for v3

markdown/dev/reference/api/utils/capitalize/en.md

@@ -0,0 +1,19 @@
+---
+title: utils.capitalize()
+---
+
+The `utils.capitalize()` function returns the string you pass it with its first
+letter turned into uppercase.
+
+## Signature
+
+```js
+String utils.capitalize(String input)
+```
+
+## Example
+
+```js
+capitalize('hello') // returns 'Hello')
+capitalize('hello there') // returns 'Hello there'
+```