Edit tasks section of the README

[Cleop]

After reading dwyl/contributing#4 about raising issues for every PR, I am creating this issue because I intend to work through the exercise on the README and then submit any amends based on my experience.

[Cleop]

• Think about order/ route of someone's learning based on resources suggested.
  Ie. Elixir School, our exercises, videos etc.
• Add line about what the README will teach you. Ie. introduce you to basic types and then run your through project set up and some basic examples. This will help readers gauge whether the README is at the right experience level for them and whether it's going to help them achieve what they're setting out to achieve.

[Cleop]

• Add a note that correct documentation will show a user how to correctly run the function. I skimmed this and got confused when implementing randomise!

• Explain basic error messages? Like:

Ie. that the randomise functions expects to receive 1 argument.

• Etiquette for documenting functions, the examples have documentation but it might be helpful to have a note saying, you should always write documentation before creating a function or devs tend to do documentation in batches or whatever the correct etiquette is!