Fix pip install command in CONTRIBUTING.md

[AhmadKhanSenpai]

Corrected the pip install command in the contribution.md file. The original command was pip -r install requirements.txt, which is incorrect. The correct command is pip install -r requirements.txt. This change ensures clarity and accuracy in the instructions for installing project dependencies.

Changes Made

- pip -r install requirements.txt
- pip -r install requirements-dev.txt
+ pip install -r requirements.txt
+ pip install -r requirements-dev.txt