Wrap INSTALL to 80 columns

INSTALL

 * Prerequisites
 
-  1. Make sure you have bison (http://www.gnu.org/software/bison/) installed in your system.
+  1. Make sure you have bison (http://www.gnu.org/software/bison/) installed in
+     your system.
   2. Make sure you have ruby installed in your system (required to build).
 
+
 * Compilation and Installation
 
   1. Run make in the top directory.
 
-     This command will create a build directory with a directory for the host environment
-     and one for each crossbuild environment based on the settings in the build_config.rb
-     file.
+     This command will create a build directory with a directory for the host
+     environment and one for each crossbuild environment based on the settings
+     in the build_config.rb file.
 
-     Assuming a default build, each of the environment directories will have the following
-     important directories:
+     Assuming a default build, each of the environment directories will have
+     the following important directories:
 
        * bin - The binary executables for this environment
        * lib - The libraries for this environment
 
-     You can find the header files in the include directory at the root of the project.
+     You can find the header files in the include directory at the root of the
+     project.
 
      You can directly invoke 'minirake' with the following command:
 
-        $ ruby ./minirake
+         $ ruby ./minirake
 
 If an error occurs when compiling mruby, it will be helpful for others if you
 send a detailed report to the developers that includes the error log, machine,
@@ -30,19 +33,19 @@ and OS type.
 
 * Adding existing gems
 
-Gems from the [list of mruby gems](http://www.mruby.org/libraries/) can be added by adding
-their respective GitHub URLs to build_config.rb. For example, to add implementations of the
-File and IO Ruby core classes to mruby, insert the following in build_config.rb under the
-comment section `Use mrbgems`:
+Gems from the [list of mruby gems](http://www.mruby.org/libraries/) can be
+added by adding their respective GitHub URLs to build_config.rb. For example,
+to add implementations of the File and IO Ruby core classes to mruby, insert
+the following in build_config.rb under the comment section `Use mrbgems`:
 
     conf.gem :git => 'git@github.com:iij/mruby-io.git', :branch => 'master'
 
-    Afterwards, re-run:
+Afterwards, re-run:
 
-        ruby ./minirake
+    ruby ./minirake
 
 
 * Porting to other platforms
 
-
 That's all.
+