📖 add contributing file

CONTRIBUTING.md

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+Contributing to Flutter Icons
+=======================
+
+We invite you to contribute to Flutter Icons! Please read the following sections
+
+---------------------------------
+
+Quality Assurance
+-----------------
+
+One of the most useful tasks, closely related to triage, is finding and filing bug reports. Testing
+beta releases, looking for regressions, creating test cases, adding to our test suites, and
+other work along these lines can really drive the quality of the product up. Creating tests
+that increase our test coverage, writing tests for issues others have filed, all these tasks
+are really valuable contributions to open source projects.
+
+Developing for Flutter Icon
+----------------------
+
+If you would prefer to create some cool design for extensions that i might forgot, don't hesitate to fork the repo and submit a pull request, it will be checked by Antoine and if it correspond to the norm you're icon will appear in the next version of the vscode extension.
+
+### Branching and Merging
+
+- Do not push directly to the main branch.
+- Create a branch related to the current issue and make a pull request (PR) to merge the branch.
+- At least one person must approve the PR before it can be merged.
+
+To develop for Flutter icon, you will eventually need to become familiar
+with our processes and conventions. This section lists the documents
+that describe these methodologies. The following list is ordered: you
+are strongly recommended to go through these documents in the order
+presented.
+
+the name of the branch must be the number of the issue followed by the name of the issue with a gitmoji that explian expilicitly the change.
+
+
+Here's an example of a valid PR message: `🔀 Add [ICON_NAME]`
+
+# commit norm:
+
+- :globe_with_meridians: = Docker & Virtual Env
+- :sparkle: = to new features in the workspace
+- :test_tube: = test politics
+- :see_no_evil: = add ignore file
+- :art: = improve some functions
+- :bug: = fix some bugs
+- :memo: = update documentation
+- :construction: = start to build new feature
+- :heavy_minus_sign: = remove code or file/folder
+- :bricks: = split functions
+- :adhesive_bandage: = norm code
+
+