Create CONTRIBUTING md

Author: anoop-76

CONTRIBUTING.md

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+## Contributing
+
+1. Familiarize yourself with the codebase by reading the [wiki](wiki).
+1. Create a new issue before starting your project so that we can keep track of
+   what you are trying to add/fix. That way, we can also offer suggestions or
+   let you know if there is already an effort in progress.
+1. Fork this repository.
+1. The [README](README.md) has details on how to set up your environment.
+1. Create a _topic_ branch in your fork based on the correct branch (usually the **develop** branch, see [Branches section](#branches) below). Note, this step is recommended but technically not required if contributing using a fork.
+1. Edit the code in your fork.
+1. Sign CLA (see [CLA](#cla) below)
+1. Send us a pull request when you are done. We'll review your code, suggest any
+   needed changes, and merge it in.
+
+### CLA
+
+External contributors will be required to sign a Contributor's License
+Agreement. You can do so by going to https://cla.salesforce.com/sign-cla.
+
+## Branches
+
+- We work in `develop`.
+- Our released (aka. _production_) branch is `master`.
+- Our work happens in _topic_ branches (feature and/or bug-fix).
+  - feature as well as bug-fix branches are based on `develop`
+  - branches _should_ be kept up-to-date using `rebase`
+  - see below for further merge instructions
+
+### Merging between branches
+
+- We try to limit merge commits as much as possible.
+
+  - They are usually only ok when done by our release automation.
+
+- _Topic_ branches are:
+
+  1. based on `develop` and will be
+  1. squash-merged into `develop`.
+
+- Hot-fix branches are an exception.
+  - Instead we aim for faster cycles and a generally stable `develop` branch.
+
+### Merging `develop` into `master`
+
+- When a development cycle finishes, the content of the `develop` branch will become the `master` branch
+
+```
+$ git checkout master
+$ git reset --hard develop
+$
+$ # Using a custom commit message for the merge below
+$ git merge -m 'Merge -s our (where _ours_ is develop) releasing stream x.y.z.' -s ours origin/master
+$ git push origin master
+```
+
+## Pull Requests
+
+- Develop features and bug fixes in _topic_ branches.
+- _Topic_ branches can live in forks (external contributors) or within this repository (committers).
+  \*\* When creating _topic_ branches in this repository please prefix with `<developer-name>/`.
+
+### Merging Pull Requests
+
+- Pull request merging is restricted to squash & merge only.