Provide an appdata file

Created by: bochecha

We'll need that if we want to appear in app stores like the brand new GNOME Software.

These should be a good basis:

• Cangjie

<?xml version="1.0" encoding="UTF-8"?>
<application>
  <id type="inputmethod">cangjie.xml</id>
  <licence>CC0</licence>
  <name>Cangjie</name>
  <summary>Cangjie input method<summary>
  <description>
    <p>Cangjie is a radical-based input method, designed to input both Traditional and Simplified Chinese, as well as Japanese.</p>
    <p>As it is rarely used outside of Hong Kong (where it is one of the two most used input methods), we strive to provide the best input experience for people of the SAR by default, but provide useful options for others.</p>
  </description>
  <url type="homepage">http://cangjians.github.io/projects/ibus-cangjie/</url>
</application>

• Quick

<?xml version="1.0" encoding="UTF-8"?>
<application>
  <id type="inputmethod">quick.xml</id>
  <licence>CC0</licence>
  <name>Quick</name>
  <summary>Quick Input Method<summary>
  <description>
    <p>Quick (also known as “Simplified Cangjie”) is a radical-based input method, designed to input both Traditional and Simplified Chinese, as well as Japanese.</p>
    <p>As it is rarely used outside of Hong Kong (where it is one of the two most used input methods), we strive to provide the best input experience for people of the SAR by default, but provide useful options for others.</p>
  </description>
  <url type="homepage">http://cangjians.github.io/projects/ibus-cangjie/</url>
</application>

Both will need to be translated (itstool seems to be the right thing to use).

Both might need icons (at least 48x48) and screenshots.

When this is done, be sure to let Richard Hughes know, so he can update his tracking document and/or his temporary repository.