add examples to README.md

Author: bicycle1885

README.md

@@ -9,8 +9,41 @@ TranscodingStreams.jl
 
 ![TranscodingStream](/docs/src/assets/transcodingstream.png)
 
-TranscodingStreams.jl is a package for transcoding data streams. Transcoding can
-be any codec. The following packages support the interfaces of this package:
+TranscodingStreams.jl is a package for transcoding data streams. There are two
+kinds of APIs:
+```julia
+using TranscodingStreams, CodecZlib
+
+# Some text.
+text = """
+Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aenean sollicitudin
+mauris non nisi consectetur, a dapibus urna pretium. Vestibulum non posuere
+erat. Donec luctus a turpis eget aliquet. Cras tristique iaculis ex, eu
+malesuada sem interdum sed. Vestibulum ante ipsum primis in faucibus orci luctus
+et ultrices posuere cubilia Curae; Etiam volutpat, risus nec gravida ultricies,
+erat ex bibendum ipsum, sed varius ipsum ipsum vitae dui.
+"""
+
+# Streaming API.
+stream = IOBuffer(text)
+stream = TranscodingStream(GzipCompression(), stream)
+stream = TranscodingStream(GzipDecompression(), stream)
+for line in eachline(stream)
+    println(line)
+end
+close(stream)
+
+# Array API.
+array = Vector{UInt8}(text)
+array = transcode(GzipCompression(), array)
+array = transcode(GzipDecompression(), array)
+@assert text == String(array)
+```
+
+Each codec has an alias for its transcoding stream type. For example,
+`GzipCompressionStream{S} = TranscodingStream{GzipCompression,S} where S<:IO`.
+
+The following packages support the interfaces of TranscodingStreams.jl:
 - [CodecZlib.jl](https://github.com/bicycle1885/CodecZlib.jl)
 - [CodecBzip2.jl](https://github.com/bicycle1885/CodecBzip2.jl)
 - [CodecXz.jl](https://github.com/bicycle1885/CodecXz.jl)