manuals: start of documentation standards document

This first version specifies how to create consistent SGV graphics

(From yocto-docs rev: 370b9e34e9092c9eed22df2e8b2d0bb979487e5c)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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+# Standards for contributing to Yocto Project documentation
+
+This document attemps to standardize the way the Yocto Project
+documentation is created.
+
+It is currently a work in progress.
+
+## Text standards
+
+This section has not been filled yet
+
+## ReStructured Text Syntax standards
+
+This section has not been filled yet
+
+## Adding screenshots
+
+The preferred format for adding screenshots is
+[Portable Network Graphics (PNG)](https://en.wikipedia.org/wiki/Portable_Network_Graphics).
+Compared to the JPEG format, PNG is lossless and compresses screenshots better.
+
+Screenshots are stored in a `figures/` subdirectory.
+
+To include a screenshot in PNG format:
+
+    .. image:: figures/user-configuration.png
+       :align: center
+
+Depending on the size of the image, you may also shrink it
+to prevent it from filling the whole page width:
+
+       :scale: 50%
+
+For some types of screenshots, for example showing
+programs displaying photographs or playing video, the JPEG
+format may be more appropriate, because it is better at
+compressing real-life images:
+
+    .. image:: figures/vlc.jpg
+       :align: center
+       :scale: 75%
+
+## Adding new diagrams
+
+New diagrams should be added in
+[Scalable Vector Graphics (SVG) format](https://en.wikipedia.org/wiki/Scalable_Vector_Graphics).
+Thanks to this, diagrams render nicely at any zoom level on generated documentation,
+instead of being pixelated.
+
+The recommended tool for creating SVG diagrams for the Yocto Project
+documentation is [Inkscape](https://inkscape.org/).
+
+### Colors
+
+The "GNOME HIG Colors" palette is used in our diagrams
+(get it from <https://gitlab.gnome.org/Teams/Design/HIG-app-icons/-/blob/master/GNOME%20HIG.gpl>
+if you don't get it from Inkscape).
+
+It's easier to use than the default one in Inkscape,
+as it has fewer but sufficient colors. This is a way
+to guarantee that we use consistent colors across the
+diagrams used in our documentation.
+
+See <https://inkscape-manuals.readthedocs.io/en/latest/palette.html>
+for details about working with color palettes in Inkscape.
+
+### Template diagram
+
+The `template/` directory contains a `template.svg` file
+to make it easier to create diagrams.
+In particular, you can use it to copy standard text, shapes,
+arrows and clipart to the new SVG document.
+
+### Fonts
+
+The recommended font for description text and labels is `Nimbus Roman`, size 10.
+Labels are in bold.
+
+`template.svg` contains ready-to-copy labels.
+
+### Text boxes
+
+Text boxes are rectangle boxes, with rounded corners, and contain centered text
+or labels. Their stroke color is slightly darker than their fill color.
+
+See `template.svg` for example boxes with different colors, which are ready
+to be reused.
+
+### Clipart
+
+Only [Public Domain](https://en.wikipedia.org/wiki/Public_domain)
+files are accepted for clipart. [Openclipart](https://openclipart.org)
+is the best known and recommended source of such clipart.
+
+It is also required to state the source of each new clipart in the commit log,
+to make it possible to check its origin.
+
+For the sake of consistency across diagrams, we recommend
+to use existing cliparts, whenever possible.
+
+If cliparts in `template.svg` do not satisfy your requirements, you can
+add to said file new cliparts, from e.g. Openclipart. Newly added
+cliparts shall stay consistent in style and color with existing ones.