Create CONTRIBUTING.md (#2191)

* Create CONTRIBUTING.md

* Update README.md

Added guide for new contributors

* Update CONTRIBUTING.md

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update CONTRIBUTING.md

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update README.md

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update CONTRIBUTING.md

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update CONTRIBUTING.md

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update CONTRIBUTING.md

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update README.md

updated link to CONTRIBUTING.md

* Update README.md

updated link to CONTRIBUTING.md

* Update README.md

* Update README.md

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update README.md

Reposition contributing guide

* Update CONTRIBUTING.md

removed verilog guide

Co-authored-by: Megan Wachs <megan@sifive.com>

* Update README.md

Added verilog tutorial link to useful resources area.

Co-authored-by: Megan Wachs <megan@sifive.com>