updated the pre-requisite para for more clarity

[wuodland]

Added the part of picking one of the courses below before all the courses are listed on line #400. Removed the "PS" part below line #407

[ericdouglas]

@wuodland thank you for your help! 🙏

Could you also make more two things?

• Bump our Curriculum Version to 1.2.3 here, because you're "fixing" our file.

• Add a little explanation in our CHANGELOG file, saying what you're doing. More explanations about CHANGELOG files here. The text will be something like this:

  ## [1.2.3] 2015-10-12
  
  ### Changed
  - Updated the prerequisite section for more clarity
  

[wuodland]

@ericdouglas Thanks. I've made a separate PR fur the changelog & also changed the main version number in the readme file.

This is my first pull-req, ty for guiding me :)

[ericdouglas]

@wuodland ok, no problem! You did a great work, thank you for helping us! 😄