Issue #1539940 by jwilson3, infiniteluke, mrf, ryanissamson: Fix up README files to encourage good placement of themes, modules, and profiles
Issue #22336 by quicksketch, scor, boombatower, and rfay. Move all core Drupal files under a core subdirectory.
#607028 by deviantintegral, marcvangend, uNeedStuff, jhodgdon, mokko, et al: Add README.txt to core. Provides some general information about Drupal and pointers to important reference pages.