add importing modules tutorial and challenge

[sabderemane]

1. This pull request resolves #79

2. Description

• add tutorial for importing a module
• add challenge for importing a module

3. Fill in checklist by marking [x]

• [x] I've read the CONTRIBUTING.md
• [x] I was assigned to this issue
• [x] My code is formatted using required linting
• [x] I've run my code locally and checked it works

[funbeedev]

@sabderemane nice tutorial. thanks :)