doc: add install document

Author: kou

README.md

@@ -20,13 +20,11 @@ The user-friendly API is implemented top of low-level libxml2 API.
 
 ## Install
 
-```console
-% luarocks install xmlua
-```
+See [online document](https://clear-code.github.io/xmlua/install/).
 
 ## Usage
 
-See [online document](https://clear-code.github.io/xmlua/).
+See [online document](https://clear-code.github.io/xmlua/tutorial/).
 
 ## Authors
 

docs/install/index.md

@@ -0,0 +1,50 @@
+---
+title: Install
+---
+
+# Install
+
+This document how to install XMLua on the following platforms:
+
+  * [Debian GNU/Linux](#debian)
+
+  * [Ubuntu](#ubuntu)
+
+  * [CentOS](#centos)
+
+  * [macOS](#macos)
+
+You must install [LuaJIT][luajit] and [LuaRocks][luarocks] before installing XMLua.
+
+## Debian GNU/Linux {#debian}
+
+```console
+% sudo apt install -y -V libxml2
+% sudo luarocks install xmlua
+```
+
+## Ubuntu {#ubuntu}
+
+```console
+% sudo apt install -y -V libxml2
+% sudo luarocks install xmlua
+```
+
+## CentOS {#centos}
+
+```console
+% sudo yum install -y libxml2
+% sudo luarocks install xmlua
+```
+
+## macOS {#macos}
+
+```console
+% brew install libxml2
+% sudo luarocks install xmlua
+```
+
+
+[luajit]:http://luajit.org/
+
+[luarocks]:https://luarocks.org/