Fix npm commands

[A-K-O-R-A]

Description

This PR corrects the wrong npm commands in the CONTRIBUTING.md file. Running npm useFF will throw an error as the correct command is npm run useFF.

References

Unknown command: "useFF"

Did you mean this?
    npm run useFF # run the "useFF" package script

To see a list of supported npm commands, run:
  npm help

Type of change

• [x] Bug fix (non-breaking change which fixes a bug)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that might cause existing functionality to not work as expected)

[OliEfr]

Thanks @A-K-O-R-A for noticing this bug and reporting it! Have a good day.