docs: add 'Importing Fonts'

docs/importing_resources/importing_fonts.rst

@@ -1,7 +1,45 @@
+===============
 Importing Fonts
 ===============
 
+Crown can import fonts from popular font file formats. Importing a font produces
+a ``.font`` resource (a map of glyphs), an accompanying ``.texture`` resource
+(an atlas containing all the glyphs) and a ``.material`` resource suitable for
+drawing text.
+
 .. figure:: images/import_font.png
    :align: center
 
-   The font import dialog.
+   The Import Font dialog.
+
+Dialog overview
+===============
+
+On the left, the importer shows a preview of the final texture atlas. On the
+right you can set various parameters that control which characters are included
+in the atlas and their size. This size does not have to match the size used when
+drawing text, but it is good practice to keep them similar to avoid scaling
+artifacts.
+
+Renaming the font
+=================
+
+Font files are often named with variants and other details embedded in the
+filename. If you prefer a simpler name, you can rename the font before
+importing by entering it in the ``Name`` field.
+
+Atlas generation
+================
+
+The atlas dimensions are shown in ``Atlas size``. They are determined
+automatically from the font ``Size`` and the selected ``Charset``. Enter the
+desired font size and press ``Enter``; Crown will regenerate the atlas and
+update the preview. Glyphs are packed as tightly as possible to keep the
+atlas small and avoid runtime performance issues.
+
+Custom charset
+==============
+
+By default Crown provides several common character sets in the ``Charset``
+dropdown. For a custom range, use ``Range min`` and ``Range max`` to set the
+first and last Unicode code point to include in the font.