init commit, with sample code

SFML/examples/shader/resources/billboard.frag

@@ -0,0 +1,11 @@
+#version 150
+
+uniform sampler2D texture;
+
+in vec2 tex_coord;
+
+void main()
+{
+    // Read and apply a color from the texture
+    gl_FragColor = texture2D(texture, tex_coord);
+}