Add current_app to docs

Author: bootstraponline

docs/docs.md

@@ -47,6 +47,7 @@ iOS uses accessibility label with a fallback to text.
 - `(Array<Element>) names(name)` Returns all elements containing name.
 - `(Element) text(text)` Returns the first element containing text.
 - `(Array<Element>) texts(text)` Returns all elements containing text.
+- `current_app` Returns information about the current app. Android only.
 
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