Update docs for trunc format helper

README.md

@@ -116,6 +116,7 @@ playerctl metadata --format "Volume: {{ volume * 100 }}"
 | `markup_escape` | string           | Escape XML markup characters in the string.                        |
 | `default`       | any, any         | Print the first value if it is present, or else print the second.  |
 | `emoji`         | status or volume | Try to convert the variable to an emoji representation.            |
+| `trunc`         | string, int      | Truncate string to a maximum length.                               |
 
 | Variable     | Description                                       |
 | ------------ | ------------------------------------------------- |

doc/playerctl.1.in

@@ -251,6 +251,12 @@ to an emoji representation. Currently implemented for
 .Fa status
 and
 .Fa volume .
+.It Fn trunc str len
+Truncate
+.Fa str
+to a maximum of
+.Fa len
+characters, adding an ellipsis (…) if necessary.
 .El
 .Pp
 The template language is also able to perform basic math operations.