Add "graphics" category

This category seems strangely missing and is already pretty well represented.

Author: raphlinus

src/boot/categories.toml

@@ -233,6 +233,13 @@ category. Libraries to help create video games are in the \
 Game engines category.\
 """
 
+[graphics]
+name = "Graphics"
+description = """
+Crates for graphics libraries and applications, including raster and vector \
+graphics primitives such as geometry, curves, and color.\
+"""
+
 [gui]
 name = "GUI"
 description = """