Reconsidering Contribution Policy/Standard

[KoukiHama]

We need to reconsider the contribution policy to be more neutral and rational.

The following documents may be useful for reference.

https://eclipse.dev/sw360/docs/development/dev-dod-and-style/#policy
https://github.com/eclipse-sw360/sw360/blob/62829f44cd8feacc1a831703a53c6614f861f1b1/CONTRIBUTING.md
https://github.com/eclipse-sw360/sw360/blob/62829f44cd8feacc1a831703a53c6614f861f1b1/CODE_OF_CONDUCT.md

https://docs.github.com/articles/github-community-guidelines

[KoukiHama]

Outdated URLs

sw360/CONTRIBUTING.md

Lines 97 to 98 in 62829f4

	* Definition of Done and code style considerations: https://github.com/eclipse/sw360/wiki/Dev-DoD-and-Style
	* Commit message format: https://github.com/eclipse/sw360/wiki/Dev-Semantic-Commits

sw360/CONTRIBUTING.md

Line 137 in 62829f4

* The slack channel and more coordinates can be found here: https://github.com/eclipse/sw360/wiki#getting-started