minor change in pixel package doc

doc.go

 // Package pixel implements platform and backend agnostic core of the Pixel game development
 // library.
 //
-// It contains the core Target, Triangles, Picture pattern and implements standard elements, such as
-// Sprite, Batch, Vec, Rect and RGBA in addition to the basic Triangles and Picture implementations:
-// TrianglesData and PictureData.
+// It specifies the core Target, Triangles, Picture pattern and implements standard elements, such
+// as Sprite, Batch, Vec, Rect and RGBA in addition to the basic Triangles and Picture
+// implementations: TrianglesData and PictureData.
 package pixel