Update README.md

Author: twadleigh

README.md

@@ -5,15 +5,28 @@
 
 Saving and loading of OpenEXR files.
 
-Basic usage:
+# Load an EXR file
+
 ```jl
 using OpenEXR
 
-# read an EXR file into an `Array{RGBA{Float16},2}`.
-myimage = OpenEXR.load(File{DataFormat{:EXR}}("myimage.exr"))
+myimage = OpenEXR.load("myimage.exr")
+```
+
+`myimage` has type `Array{T,2}` where `T` is one of:
+
+- RGBA{Float16}
+- RGB{Float16}
+- GrayA{Float16}
+- Gray{Float16}
 
-# save an image to an EXR file
-OpenEXR.save(File{DataFormat{:EXR}}("myimage2.exr"), myimage)
+depending on which channels are present in the file.
+
+# Save an image as an EXR file
+
+```jl
+OpenEXR.save("myimage2.exr", myimage)
 ```
 
-TODO: get this registered with [FileIO](https://github.com/JuliaIO/FileIO.jl).
+`myimage` can be any subtype of `AbstractArray{C,2}` where `C` is any color type defined in
+[ColorTypes.jl](https://github.com/JuliaGraphics/ColorTypes.jl).