Feature/add contributions (#10)

* Add a CONTRIBUTION file

* Some changes

* Even more changes

CONTRIBUTIONS.md

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+# Welcome to GitHub docs contributing guide <!-- omit in toc -->
+Thank you for investing your time in contributing to our project! <!-- Any contribution you make will be reflected on [docs.github.com](https://docs.github.com/en)--> :sparkles:. In this guide you will get an overview of the contribution workflow from opening an issue, creating a PR, reviewing, and merging the PR.
+
+## New contributor guide
+
+To get an overview of the AccordDaTools, read the [README](README.md).
+
+Here are some resources to help you get started with open source contributions:
+
+- [Finding ways to contribute to open source on GitHub](https://docs.github.com/en/get-started/exploring-projects-on-github/finding-ways-to-contribute-to-open-source-on-github)
+- [Set up Git](https://docs.github.com/en/get-started/quickstart/set-up-git)
+- [GitHub flow](https://docs.github.com/en/get-started/quickstart/github-flow)
+- [Collaborating with pull requests](https://docs.github.com/en/github/collaborating-with-pull-requests)
+
+### Issues
+#### Create a new issue
+If you spot a problem , [search if an issue already exists](https://github.com/Hirlam/AccordDaTools/issues). If a related issue doesn't exist, you can open a new issue using a relevant [issue form](https://github.com/Hirlam/AccordDaTools/issues/new/choose).
+
+#### Solve an issue
+If you find an issue to work on, you are welcome to open a PR with a fix!
+
+### Make Changes
+#### Make changes in the UI
+Click **Make a contribution** at the bottom of any docs page to make small changes such as a typo, sentence fix, or a broken link. This takes you to the `.md` file where you can make your changes and [create a pull request](#pull-request) for a review. 
+
+Scan through [existing issues](https://github.com/Hirlam/AccordDaTools/issues) to find one that interests you. You can narrow down the search using `labels` as filters. As a general rule, we don’t assign issues to anyone. If you find an issue to work on, you are welcome to open a PR with a fix.
+
+#### Make changes locally - fork & branch
+1. Fork the repository: [Fork the repo](https://docs.github.com/en/github/getting-started-with-github/fork-a-repo#fork-an-example-repository) so that you can make your changes without affecting the original project until you're ready to merge them.
+2. Create a working branch and start with your changes!
+
+### For developers
+The following requirements should be kept in mind by developers:
+#### Installation
+AccordDaTools makes use of [https://cmake.org/](CMake) to configure and install the code. Your new developments should be captured by the CMake insfrastructure.
+#### Execution
+ - All new tools should have a built-in help option: `$~> new_da_tool -h` that provides some brief instructions on how to use the tool.
+ - In general, AccordDaTools have data-processing scripts and plotting scripts. Try to avoid anything in between!
+ - All options should be provided via the command-line interface (CLI)
+ - No Python version 2 allowed!
+
+### Commit your update
+Commit the changes once you are happy with them. See [Atom's contributing guide](https://github.com/atom/atom/blob/master/CONTRIBUTING.md#git-commit-messages) to know how to use emoji for commit messages. Once your changes are ready, don't forget to [self-review](/contributing/self-review.md) to speed up the review process:zap:.
+
+### Pull Request
+When you're finished with the changes, create a pull request, also known as a PR.
+- Fill the "Ready for review" template so that we can review your PR. This template helps reviewers understand your changes as well as the purpose of your pull request. 
+- Don't forget to [link PR to issue](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue) if you are solving one.
+- Enable the checkbox to [allow maintainer edits](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/allowing-changes-to-a-pull-request-branch-created-from-a-fork) so the branch can be updated for a merge.
+Once you submit your PR, a Docs team member will review your proposal. We may ask questions or request for additional information.
+- We may ask for changes to be made before a PR can be merged, either using [suggested changes](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/incorporating-feedback-in-your-pull-request) or pull request comments. You can apply suggested changes directly through the UI. You can make any other changes in your fork, then commit them to your branch.
+- As you update your PR and apply changes, mark each conversation as [resolved](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/commenting-on-a-pull-request#resolving-conversations).
+- If you run into any merge issues, checkout this [git tutorial](https://lab.github.com/githubtraining/managing-merge-conflicts) to help you resolve merge conflicts and other issues.
+
+### Your PR is merged!
+
+Congratulations :tada::tada: The AccordDaTools team thanks you :sparkles:. 
+
+Once your PR is merged, your contributions will be publicly visible on the [AccordDaTools](https://github.com/Hirlam/AccordDaTools)