docs: include Windows guide for custom fonts

[wrong7]

This commit also includes information about the importance of creating a single texture and generating the charset file.

Changed the following command can be used to remove overlaps to the overlaps need to be removed since there is no command for Windows.

Added 5-step guide to achieve the same result as in Linux.

Added an example charset.txt (currently the default for uikit).

Fixed a typo in the msdf-bmfont command to use the same filename as the generated from fontforge in the previous step.

Added an important note to generate only 1 texture for each font.

[bbohlender]

@wrong7 thank you very much 🙏🏼