Added an INSTALL section to the README.
Fixed the jruby build script to use the binary archive.
Added the md5 for jruby-bin-1.7.4.tar.gz.
Made jruby 1.7.4 the stable version.
Fixed a typo.
Extract jruby-bin directly into the $INSTALL_DIR.
Recommend using sudo for make install.
Added an Endorsements section.
Fixed the $RUBY_SRC_DIR for rubinius.