Removed config instructions that no longer work
Corrected the rbx version names in the option descriptions
So far as I can tell, the default mode is now 1.9 (updated the readme)
Corrected a spelling mistake (follwing => following)
Removed reference to switching language mode
Merge pull request #2528 from iainbeeston/update_build_instructions

Updated build instructions in the README to reflect what happens in ./configure