docs(project): add fleshed out contributing.md

CONTRIBUTING.md

@@ -0,0 +1,65 @@
+## I want to...
+
+### Submit a bug report
+
+- Make sure you can reproduce it in the latest version of GitGuardian Shield.
+- Open an issue on the [issue tracker](https://github.com/GitGuardian/gg-shield/issues).
+
+### Fix an open and confirmed bug
+
+- This bug will have a `confirmed` tag on the issue tracker.
+- Leave a message on the issue tracker that you're interested in
+  fixing this bug.
+
+### Propose a new feature
+
+- Open an issue on the [issue tracker](https://github.com/GitGuardian/gg-shield/issues).
+
+### Implement a new CI integration
+
+- Open an issue on the [issue tracker](https://github.com/GitGuardian/gg-shield/issues).
+- No core contributor review is necessary on this feature.
+- Submit a Pull request
+
+### Implement a new feature
+
+- Follow `Propose a new feature`
+- A core contributor will work out with you if it's the project's vision
+  and some rudimentary specs
+- Submit a Pull request
+
+## Setup your development environment
+
+1. Install pipenv (https://github.com/pypa/pipenv#installation)
+
+1. Install the pre-commit framework (https://pre-commit.com/#install)
+
+1. Fork and clone the repository
+
+1. Install dev packages and environment
+
+   ```sh
+   $ pipenv install --dev
+   ```
+
+1. Install pre-commit hooks
+
+   ```sh
+   $ pre-commit install
+   ```
+
+## Style guides
+
+### Git commit message
+
+- Use the present tense ("Add feature" not "Added feature")
+- Use the imperative mood ("Move cursor to..." not "Moves cursor to...")
+- [Use conventional commit messages](https://www.conventionalcommits.org/en/v1.0.0/#commit-message-with-scope), examples:
+  - feat(integration): Add Azure Pipelines support
+  - fix(ggshield): add pre-push mode header
+
+### Python
+
+- We're committed to support python 3.6+ for now
+- Document new functions added if they're not obvious
+- Black, flake and isort should keep the rest of your code standard

README.md

@@ -799,16 +799,6 @@ $ ggshield scan pre-commit
 Lines that are too long are truncated to match the size of the terminal,
 unless the verbose mode is used (`-v` or `--verbose`).
 
-# Contributing
-
-If you have questions you would like to ask the developers,
-or feedback you would like to provide,
-feel free to create an issue on our issue tracker.
-
-We would love to hear from you.
-Additionally, if you have a feature you would like to suggest,
-feel free to create an issue on our issue tracker.
-
 # Related open source projects
 
 - [truffleHog](https://github.com/dxa4481/truffleHog)

SECURITY.md

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+## Reporting a vulnerability
+
+By preference:
+
+- Send an email to support@gitguardian.com
+- Send an email to a core contributor directly
+
+If you get no response in the next 2 business days, try another avenue of communication, we are very committed to providing quick follow-up on vulnerability reports.