doc: Improve comments

ebitenutil/loadimage.go

@@ -29,7 +29,7 @@ import (
 // How to solve path depends on your environment. This varies on your desktop or web browser.
 // Note that this doesn't work on mobiles.
 //
-// Instead of using this function, it is safer to embed your resources, e.g., with github.com/jteeuwen/go-bindata .
+// For productions, instead of using this function, it is safer to embed your resources, e.g., with github.com/jteeuwen/go-bindata .
 func NewImageFromFile(path string, filter ebiten.Filter) (*ebiten.Image, image.Image, error) {
 	file, err := OpenFile(path)
 	if err != nil {

ebitenutil/shapes.go

@@ -41,7 +41,7 @@ func colorScale(clr color.Color) (rf, gf, bf, af float64) {
 	return
 }
 
-// DrawLine draws a line on the given destination dst.
+// DrawLine draws a line segment on the given destination dst.
 //
 // DrawLine is intended to be used mainly for debugging or prototyping purpose.
 func DrawLine(dst *ebiten.Image, x1, y1, x2, y2 float64, clr color.Color) {

mobile/mobile.go

@@ -39,6 +39,8 @@ func Start(f func(*ebiten.Image) error, width, height int, scale float64, title
 // On Android, this should be called at onDrawFrame of Renderer (used by GLSurfaceView).
 //
 // On iOS, this should be called at glkView:drawInRect: of GLKViewDelegate.
+//
+// Update returns error when 1) OpenGL error happens, or 2) f in Start returns error samely as ebiten.Run.
 func Update() error {
 	return update()
 }

text/text.go

@@ -15,6 +15,8 @@
 // Package text offers functions to draw texts on an Ebiten's image.
 //
 // Note: This package is experimental and API might be changed.
+//
+// For the example using a TTF font, see font package in the examples.
 package text
 
 import (