updated docs

Author: oscarotero

docs/4.syntax/2.pipes.md

@@ -36,6 +36,7 @@ The `empty` filter checks if the variable is empty and returns a boolean. A vari
 - It's considered `false` in JavaScript (the value is `false`, an empty string, `0`, `null`, `undefined`, etc)
 - It's a string only with spaces (For example `" \t\n"`)
 - I'ts an empty array (`[]`)
+- I'ts an empty plain object (`{}`)
 
 This filter is useful for conditions:
 
@@ -45,6 +46,14 @@ No tags defined
 {{ /if }}
 ```
 
+Use exclamation mark to check if a value is not empty:
+
+```vto
+{{ if tags |> !empty }}
+There are tags
+{{ /if }}
+```
+
 The `safe` filter does not transform the content, but can be used to mark HTML
 data as trusted when in autoescaping mode;