Update README.md as per template
Update README.md as per template

What's changed:
1. s/line-bot-sdk-php/LINE Messaging API SDK for PHP/
2. Add Introduction section
3. s/About the LINE Messaging API/Documentation/
4. Move up "Requirements" section before "Installation" section
5. Add "Help and media" section
6. Add "Versioning section"
7. Add "Contributing" section. Move hacking guide under "Contributing" section.
8. Reorganised License section as per Apache License website guidelines
line/line-bot-sdk-php,line/line-bot-sdk-php