Docs for atuinsh/atuin#2286 (#69)

Documentation update for atuinsh/atuin#2286

Author: tobiasge

Diff for: src/content/docs/configuration/config.mdx

@@ -572,6 +572,7 @@ Which preview strategy is used to calculate the preview height. It respects `max
 |----------------|-----------------------------------------------------|
 | auto (default) | selected command                                    |
 | static         | longest command in the current result set           |
+| fixed          | use `max_preview_height` as fixed value             |
 
 By using `auto` a preview is shown, iff the command is longer than the width of the terminal.