Update and fix some typos and mistakes in "Contribution section of documentation and Comprehensive Installation section"

Hey @AyanSinhaMahapatra and @majurg, I think this small issue/enhancements need to be updated Please have a look!
### Description

> 1. In the contribution section of the documentation, forking steps are not included, only steps for [cloning](https://scancode-toolkit.readthedocs.io/en/latest/contribute/contrib_doc.html#setup-local-build) the project from the main repo is provided
> 2 . Comprehensive Installation section having installation via pip command section does not provide the command to Activate the Virtual Environment for windows.

### Link to Documentation Page

> [Contribution Section for documentation](https://scancode-toolkit.readthedocs.io/en/latest/contribute/contrib_doc.html#setup-local-build)
> [Comprehensive Installation](https://scancode-toolkit.readthedocs.io/en/latest/getting-started/install.html#installation-as-a-library-via-pip)

### Select Category

- [ ] Inconsistency
- [ ] New Section Request
- [X] General Improvement
- [X] Typo/Mistakes
- [ ] Other