fixes for installation & setup issues

[AhmadHakami]

in this updated version i fixed some issues with the installation and setup:

1. add mkdir checkpoints command with installation because the checkpoints folder was missing
2. while running pip install -r requirements.txt some issues arose which i resolved by specifying the python version with python==3.7.7 and installing basicsr, the error message was:

note: This error originates from a subprocess and is likely not a problem with pip
error: metadata-generation-failed

× Encountered error while generating package metadata
╰─> See above for output

note: This is an issue with the package mentioned above, not pip
hint: See above for details
WARNING: There was an error checking the latest version of pip

3. update the requirements.txt file
4. add a section for setup and installation steps in the README.md file