Update install instructions

[zbskii]

If a user installs scala-mode2 via elpa we don't want to encourage them to 'require scala-mode2' as most users will stick this in their .emacs which won't work since elpa packages are loaded after the emacs init file.

[hvesalai]

So what you are saying is that on the first start-up it will fail since the package has not been loaded yet?

Could you amend your commit so that also .sbt is added to the list of file extensions of scala-mode.

[zbskii]

@hvesalai see: http://emacswiki.org/emacs/ELPA#toc3

Most people will just drop (require 'scala-mode2) in their .emacs file; this won't work as scala-mode2 won't be defined yet.

[hvesalai]

Thank you!