docs: link to official Jinja2 extensions

Author: dannyadair

docs/configuration.md

@@ -38,7 +38,7 @@ At least `documents` has to be specified.
 | `directories.images`            | string  | `"images"`                           | Location of image files.                                                                                                                                                                                                                                                |
 | `directories.pages`             | string  | `"pages"`                            | Location of page configurations.                                                                                                                                                                                                                                        |
 | `directories.templates`         | string  | `"templates"`                        | Location of SVG template files.                                                                                                                                                                                                                                         |
-| `jinja2_extensions`             | array   | `[]`                                 | jinja2_extensions (like `jinja2.ext.do`) to load and use in templates.                                                                                                                                                                                                  |
+| `jinja2_extensions`             | array   | `[]`                                 | [Jinja2 extensions](https://jinja.palletsprojects.com/en/stable/extensions/) (like `jinja2.ext.do`) to load and use in templates.                                                                                                                                       |
 | `template_renderers`            | array   | `["render_highlight"]`               | List of automatically applied renderers. `render_highlight` is currently the only available one and enabled by default. It will replace `<highlight>...</highlight>` with `<tspan>` using the colour `style.color` to let you highlight words inside YAML text.         |
 | `template_filters`              | array   | `["wordwrap"]`                       | List of filters made available to templates. `wordwrap` is currently the only available filter. It splits text into lines so that full words have to fit within the specified total number of character for example `{% set desc_lines = item.desc \| wordwrap(40) %}`. |
 | `svg2pdf_backend`               | string  | `"cairosvg"`                         | Backend to use for SVG to PDF conversion. `"cairosvg"` is built-in, the alternative `"inkscape"` requires Inkscape to be installed                                                                                                                                      |