Documentation: Update minimum calibre-web version reference (#2412)

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Co-authored-by: shamoon <4887959+shamoon@users.noreply.github.com>

docs/widgets/services/calibre-web.md

@@ -3,7 +3,7 @@ title: Calibre-web
 description: Calibre-web Widget Configuration
 ---
 
-**Note: this widget requires a feature of calibre-web that has not yet been distributed in versioned release. The code is contained in ["nightly" lsio builds after 25/8/23](https://hub.docker.com/layers/linuxserver/calibre-web/nightly/images/sha256-b27cbe5d17503de38135d925e226eb3e5ba04c558dbc865dc85d77824d35d7e2) or running the calibre-web source code including commit [0499e57](https://github.com/janeczku/calibre-web/commit/0499e578cdd45db656da34cd2d7152c8d88ceb23).**
+**Note: widget requires calibre-web ≥ v0.6.21.**
 
 Allowed fields: `["books", "authors", "categories", "series"]`.