README: Add info

Change-Id: Iad69e17bcfebd66d59ec18724c286519b037f81c
Allow setting default language

Allow the user to set a default language. Setting the default language
changes the value in the paste layout as well, remains throughout
pastes, and between launches

Change-Id: Ia2b28bad049ff52750814593a6e921d7dea62b2d