Add sqlcipher feature to README.
Add sqlcipher feature to README.

gwenn/rusqlite,xinghun92/rusqlite,mikelodder7/rusqlcipher,xinghun92/rusqlite,mikelodder7/rusqlcipher,jgallagher/rusqlite,xinghun92/rusqlite,gwenn/rusqlite,gwenn/rusqlite,jgallagher/rusqlite,mikelodder7/rusqlcipher,jgallagher/rusqlite