Add a contribution guide (#1379)

Add contribution.md file with some details.

CONTRIBUTING.md

@@ -0,0 +1,107 @@
+# Contribution Guide
+
+* [Before you get started](#before-you-get-started)
+    * [Code of Conduct](#code-of-conduct)
+* [Your First Contribution](#your-first-contribution)
+    * [Find a good first topic](#find-a-good-first-topic)
+* [Setting up your development environment](#setting-up-your-development-environment)
+    * [Fork the project](#fork-the-project)
+    * [Clone the project](#clone-the-project)
+    * [New branch for a new code](#new-branch-for-a-new-code)
+    * [Test](#test)
+    * [Commit and push](#commit-and-push)
+    * [Create a Pull Request](#create-a-pull-request)
+    * [Sign the CLA](#sign-the-cla)
+    * [Get a code review](#get-a-code-review)
+
+## Before you get started
+
+### Code of Conduct
+
+Please make sure to read and observe our [Code of Conduct](./CODE_OF_CONDUCT.md).
+
+## Your First Contribution
+
+### Find a good first topic
+
+You can start by finding an existing issue with the
+[good first issue](https://github.com/dgraph-io/badger/labels/good%20first%20issue) or [help wanted](https://github.com/dgraph-io/badger/labels/help%20wanted) labels. These issues are well suited for new contributors.
+
+
+## Setting up your development environment
+
+Badger uses [`Go Modules`](https://github.com/golang/go/wiki/Modules)
+to manage dependencies. The version of Go should be **1.12** or above.
+
+### Fork the project
+
+- Visit https://github.com/dgraph-io/badger
+- Click the `Fork` button (top right) to create a fork of the repository
+
+### Clone the project
+
+```sh
+$ git clone https://github.com/$GITHUB_USER/badger
+$ cd badger
+$ git remote add upstream git@github.com:dgraph-io/badger.git
+
+# Never push to the upstream master
+git remote set-url --push upstream no_push
+```
+
+### New branch for a new code
+
+Get your local master up to date:
+
+```sh
+$ git fetch upstream
+$ git checkout master
+$ git rebase upstream/master
+```
+
+Create a new branch from the master:
+
+```sh
+$ git checkout -b my_new_feature
+```
+
+And now you can finally add your changes to project.
+
+### Test
+
+Build and run all tests:
+
+```sh
+$ ./test.sh
+```
+
+### Commit and push
+
+Commit your changes:
+
+```sh
+$ git commit
+```
+
+When the changes are ready to review:
+
+```sh
+$ git push origin my_new_feature
+```
+
+### Create a Pull Request
+
+Just open `https://github.com/$GITHUB_USER/badger/pull/new/my_new_feature` and
+fill the PR description.
+
+### Sign the CLA
+
+Click the **Sign in with Github to agree** button to sign the CLA. [An example](https://cla-assistant.io/dgraph-io/badger?pullRequest=1377).
+
+### Get a code review
+
+If your pull request (PR) is opened, it will be assigned to one or more
+reviewers. Those reviewers will do a code review.
+
+To address review comments, you should commit the changes to the same branch of
+the PR on your fork.

README.md

@@ -59,6 +59,7 @@ For more details on our version naming schema please read [Choosing a version](#
     + [Comparisons](#comparisons)
     + [Benchmarks](#benchmarks)
   * [Projects Using Badger](#projects-using-badger)
+  * [Contributing](#contributing)
   * [Frequently Asked Questions](#frequently-asked-questions)
 
 ## Getting Started
@@ -787,6 +788,10 @@ Below is a list of known projects that use Badger:
 
 If you are using Badger in a project please send a pull request to add it to the list.
 
+## Contributing
+
+If you're interested in contributing to Badger see [CONTRIBUTING.md](./CONTRIBUTING.md).
+
 ## Frequently Asked Questions
 ### My writes are getting stuck. Why?