Add new practice exercise: bottle-song

[jimmytty]

I set difficulty to 2 but I'm in doubt about 5. There is a lot of text in this exercise and comparing the wrong results is often very laborious/complicated.

[IsaacG]

Here's the difficulty (and number of times that difficulty is used) on other tracks for this exercise. 3 (easy) is pretty common.

      4   1
      1   2
     19   3
      5   4
      7   5
      1   6

[jimmytty]

Here's the difficulty (and number of times that difficulty is used) on other tracks for this exercise. 3 (easy) is pretty common.

      4   1
      1   2
     19   3
      5   4
      7   5
      1   6

Is it better change to 3 here too?

[selah6421-cyber]

كيفا مكن قراءة الرموز

[selah6421-cyber]

#107

[selah6421-cyber]

[IsaacG]

Is it better change to 3 here too?

No. This repo uses 2/5/8 for easy/medium/difficult. Using a 2 vs 3 has no impact on what students see.

[IsaacG]

Thanks for all your work here!