Some minor README fixes in the installation section.
Some minor README fixes in the installation section.

* Use markdown code blocks
* Clarify other-rake-tasks section
* Remove haml installation instructions. (Haml is a surveyor dependency so
  it doesn't need to be in the Gemfile separately.)

NUBIC/surveyor,lampo/surveyor,blueboard/surveyor,alanjcfs/surveyor,bricesanchez/surveyor,bricesanchez/surveyor,risuiowa/surveyor,markedmondson/surveyor,HeHStudy/surveyor,fhisamoto/surveyor,Guestfolio/surveyor,fhisamoto/surveyor,blueboard/surveyor,alanjcfs/surveyor,bricesanchez/surveyor,NUBIC/surveyor,blueboard/surveyor,markedmondson/surveyor,serracorwin/surveyor,lampo/surveyor,Guestfolio/surveyor,Guestfolio/surveyor,markedmondson/surveyor,bricesanchez/surveyor,blueboard/surveyor,HeHStudy/surveyor,serracorwin/surveyor,risuiowa/surveyor,HeHStudy/surveyor,anitsirc/surveyor,lampo/surveyor,fhisamoto/surveyor,anitsirc/surveyor,HeHStudy/surveyor,serracorwin/surveyor,alanjcfs/surveyor,lampo/surveyor,risuiowa/surveyor,anitsirc/surveyor,NUBIC/surveyor,anitsirc/surveyor,risuiowa/surveyor,alanjcfs/surveyor,Guestfolio/surveyor,fhisamoto/surveyor