Provide image formats for free open-source editors

[wks]

This repository includes templates for community posters in the .sketch, .fig and .psd file formats. All of them are proprietary formats.

However, all participants of OSPP are open-source communities, and most of us use free open-source software for our day jobs. Although some free softwares can import some of those formats, it doesn't work perfectly. For example, Krita can import the .psd format, but it does not support vector layers. It is unlikely that Krita or any other programs would ever fully support the .psd format because according to this document, .psd is an internal file format without on-line specification.

Although some proprietary softwares work better than their free counterparts, I think this poster is simple enough that free open-source image editors such as Krita, GIMP, Inkscape are powerful enough to handle it. As a program that promotes the adoption of free open-source software, OSPP should make an example by providing necessary event-organisation documents in free formats.