Uses "Vue-Admin" as project name across Readme

[tehuel]

Description

Small changes in README file to use Vue-Admin as project name.

I've decided to use this format just because of all the variations found in the README this one was the most used.

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce the cases. Please also list any relevant details for your test configuration

Checklist:

The following options in bold are required for a PR approval. Please check the boxes only if necessary, it help us minimizing the reviewing process.

• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes

[sgobotta]

Thanks @tehuel :ok_hand: I'm up to all those ideas that help the library improve it's readability. I just left a little text addition request, let me know what you think before merging.