Clean up the README

- Fix missing HTTPS on links
- Use direct link
- Add language shell to code blocks
- Use HTML5 tags

Author: jbampton

README.md

@@ -1,35 +1,35 @@
 mruby.org
 =========
 
-This is the [Jekyll](http://www.jekyllrb.com/) source of
-the [mruby.org](http://mruby.org/) website.
+This is the [Jekyll](https://jekyllrb.com/) source of
+the [mruby.org](https://mruby.org/) website.
 
 ## Preview
 
 The following will give you a preview of the site.
 
 Install bundler:
 
-```
+```shell
 gem install bundler
 ```
 
 Clone the repository:
 
-```
+```shell
 git clone https://github.com/mruby/mruby.github.io
 ```
 
 Install Jekyll and its dependencies:
 
-```
+```shell
 cd mruby.github.io
 bundle install
 ```
 
 Preview the site:
 
-```
+```shell
 bundle exec jekyll serve
 open "http://localhost:4000"
 ```

_includes/header.html

@@ -18,4 +18,4 @@
         <link rel="stylesheet" href="/css/main.css">
 
         <!-- Favicon -->
-        <link rel="icon" type="image/png" href="/favicon.png" />
+        <link rel="icon" type="image/png" href="/favicon.png">

_includes/navigation.html

@@ -1,6 +1,6 @@
             <nav class="navbar navbar-mruby" role="navigation">
               <div class="navbar-header">
-                <a href="/"><img src="/images/mruby_header.png" /></a>
+                <a href="/"><img src="/images/mruby_header.png"></a>
               </div>
 
               <div>
@@ -25,7 +25,7 @@
                 <!--
                 <form class="navbar-form navbar-left" role="search">
                   <div class="form-group">
-                    <input type="text" class="form-control" />
+                    <input type="text" class="form-control">
                   </div> <button type="submit" class="btn btn-default">Submit</button>
                 </form>
                 -->