Currently only for en_US locale. If someone wants to test another locale, let me know and I can try to provide you with the files.
A note on why this can't be a modular modification. As things are right now, script files contained in mod packages will not be loaded until a game is started (as in a getting past the Sean Bean loading screen). This means any scripts that execute on the Main Menu won't run until you first start a game and then exit, and that defeats the point of this mod.
Just unzip into the game install directory.
This modifies three of the original game files:
Civilopedia on Main Menu 1.0.0
This adds a link to the Civilopedia to the Main Menu. No more waiting on Sean Bean!