add introduction to godoc

README.md

@@ -23,7 +23,6 @@ If newer version than itself is detected, it downloads released binary from GitH
 - Many archive and compression formats are supported (zip, gzip, tar)
 
 [go-github-selfupdate]: https://github.com/rhysd/go-github-selfupdate
-[semantic versioning]: https://semver.org/
 [GitHub Releases API]: https://developer.github.com/v3/repos/releases/
 
 ## Try Out Example
@@ -117,6 +116,9 @@ Prefix before version number `\d+\.\d+\.\d+` is automatically omitted. For examp
 Tags which don't contain a version number are ignored (i.e. `nightly`). And releases marked as `pre-release`
 are also ignored.
 
+[semantic versioning]: https://semver.org/
+
+
 ### Structure of Releases
 
 In summary, structure of releases on GitHub looks like:
@@ -176,5 +178,5 @@ tj/go-update:
 
 
 
-[GoDoc]: https://godoc.org/github.com/rhysd/go-github-selfupdate
+[GoDoc]: https://godoc.org/github.com/rhysd/go-github-selfupdate/selfupdate
 

selfupdate/doc.go

@@ -0,0 +1,34 @@
+/*
+Package selfupdate provides self-update mechanism to Go command line tools.
+
+Go does not provide the way to install/update the stable version of tools. By default, Go command line tools are updated
+
+- using `go get -u` (updating to HEAD)
+- using system's package manager (depending on the platform)
+- downloading executables from GitHub release page manually
+
+By using this library, you will get 4th choice:
+
+- from your command line tool directly (and automatically)
+
+go-github-selfupdate detects the information of the latest release via GitHub Releases API and check the current version.
+If newer version than itself is detected, it downloads released binary from GitHub and replaces itself.
+
+- Automatically detects the latest version of released binary on GitHub
+- Retrieve the proper binary for the OS and arch where the binary is running
+- Update the binary with rollback support on failure
+- Tested on Linux, macOS and Windows
+- Many archive and compression formats are supported (zip, gzip, tar)
+
+There are some naming rules. Please read following links.
+
+Naming Rules of Released Binaries:
+  https://github.com/rhysd/go-github-selfupdate#naming-rules-of-released-binaries
+
+Naming Rules of Git Tags:
+  https://github.com/rhysd/go-github-selfupdate#naming-rules-of-git-tags
+
+This package is hosted on GitHub:
+  https://github.com/rhysd/go-github-selfupdate
+*/
+package selfupdate