update docs

Author: bicycle1885

README.md

@@ -6,17 +6,20 @@ TranscodingStreams.jl
 [![TravisCI Status][travisci-img]][travisci-url]
 [![codecov.io][codecov-img]][codecov-url]
 
+TranscodingStreams.jl is a package for transcoding data streams. Transcoding can
+be any codec. For example, following packages define lossless compression and
+decompression codecs:
+- [CodecZlib.jl](https://github.com/bicycle1885/CodecZlib.jl)
+- [CodecBzip2.jl](https://github.com/bicycle1885/CodecBzip2.jl)
+- [CodecXz.jl](https://github.com/bicycle1885/CodecXz.jl)
+- [CodecZstd.jl](https://github.com/bicycle1885/CodecZstd.jl)
+
+Consult the [docs][docs-latest-url] for more details and examples.
+
 [travisci-img]: https://travis-ci.org/bicycle1885/TranscodingStreams.jl.svg?branch=master
 [travisci-url]: https://travis-ci.org/bicycle1885/TranscodingStreams.jl
 [codecov-img]: http://codecov.io/github/bicycle1885/TranscodingStreams.jl/coverage.svg?branch=master
 [codecov-url]: http://codecov.io/github/bicycle1885/TranscodingStreams.jl?branch=master
 [docs-latest-img]: https://img.shields.io/badge/docs-latest-blue.svg
 [docs-latest-url]: https://bicycle1885.github.io/TranscodingStreams.jl/latest/
 
-TranscodingStreams.jl is a package for transcoding data streams. Transcoding can
-be any codec. For example, following packages define lossless compression and
-decompression codecs:
-- [CodecZlib.jl](https://github.com/bicycle1885/CodecZlib.jl)
-- [CodecZstd.jl](https://github.com/bicycle1885/CodecZstd.jl)
-- [CodecBzip2.jl](https://github.com/bicycle1885/CodecBzip2.jl)
-- [CodecXz.jl](https://github.com/bicycle1885/CodecXz.jl)

docs/src/index.md

@@ -104,13 +104,17 @@ Codecs are defined in other packages listed below:
     </tr>
 </table>
 
+Install packages you need by calling `Pkg.add(<package name>)` in a Julia
+session. For example, if you want to read gzip-compressed files, call
+`Pkg.add("CodecZlib")` to use `GzipDecompression` or `GzipDecompressionStream`.
 By convention, codec types have a name that matches `.*(Co|Deco)mpression` and
-I/O types have a codec name with `Stream` suffix.  An important thing is these
-packages depend on TranscodingStreams.jl and not *vice versa*. This means you
-can install any codec package you need without installing all codec packages.
-Also, if you want to define your own codec, it is totally feasible like these
-packages.  TranscodingStreams.jl requests a codec to implement some interface
-functions which will be described later.
+I/O types have a codec name with `Stream` suffix. All codecs are a subtype
+`TranscodingStreams.Codec` and streams are a subtype of `Base.IO`. An important
+thing is these packages depend on TranscodingStreams.jl and not *vice versa*.
+This means you can install any codec package you need without installing all
+codec packages.  Also, if you want to define your own codec, it is totally
+feasible like these packages.  TranscodingStreams.jl requests a codec to
+implement some interface functions which will be described later.
 
 
 Examples