update README.org
use @<del> rather than + to strike through multiple lines
github does not support html tag, delete this paragraph straightforward
[#34] fix theme not change issue
[#34] continue to fix theme issue, introduce a constant to represent the org-page folder, otherwise errors occurs
[#30] refine directory processing, use expand-file-name instead of file-name-as-directory to simplify code
delete unused example files