bundle the GPL3 badge with the repository to avoid an external link

README.md

@@ -14,7 +14,7 @@
 
 # OutFly
 
-[![License: GPL 3.0](https://img.shields.io/badge/license-GPL_v3.0-blue.svg)](https://www.gnu.org/licenses/gpl-3.0.html)
+[![License: GPL 3.0](doc/images/badge-gpl3.svg)](https://www.gnu.org/licenses/gpl-3.0.html)
 [![Powered by Bevy](doc/images/badge-bevy.svg)](https://bevyengine.org)
 [![Available on itch.io](doc/images/badge-itch.svg)](https://yunicode.itch.io/outfly)
 [![Donate on Liberapay](https://img.shields.io/liberapay/patrons/outfly?logo=liberapay&logoColor=%23ffffff)](https://liberapay.com/outfly)

doc/images/badge-gpl3.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="106" height="20" role="img" aria-label="license: GPL v3.0"><title>license: GPL v3.0</title><linearGradient id="s" x2="0" y2="100%"><stop offset="0" stop-color="#bbb" stop-opacity=".1"/><stop offset="1" stop-opacity=".1"/></linearGradient><clipPath id="r"><rect width="106" height="20" rx="3" fill="#fff"/></clipPath><g clip-path="url(#r)"><rect width="47" height="20" fill="#555"/><rect x="47" width="59" height="20" fill="#007ec6"/><rect width="106" height="20" fill="url(#s)"/></g><g fill="#fff" text-anchor="middle" font-family="Verdana,Geneva,DejaVu Sans,sans-serif" text-rendering="geometricPrecision" font-size="110"><text aria-hidden="true" x="245" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="370">license</text><text x="245" y="140" transform="scale(.1)" fill="#fff" textLength="370">license</text><text aria-hidden="true" x="755" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="490">GPL v3.0</text><text x="755" y="140" transform="scale(.1)" fill="#fff" textLength="490">GPL v3.0</text></g></svg>