docs(contrib): add guidelines

CONTRIBUTING.md

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+# Contributing Guidelines
+
+Some basic conventions for contributing to this project.
+
+### General
+
+Please make sure that there aren't existing pull requests attempting to address the issue mentioned. Likewise, please check for issues related to update, as someone else may be working on the issue in a branch or fork.
+
+* Non-trivial changes should be discussed in an issue first
+* Develop in a topic branch, not master
+* Squash your commits
+
+### Branching
+
+**Branch naming conventions**
+
+* Use grouping tokens (words) at the beginning of your branch names.
+* Define and use short lead tokens to differentiate branches in a way that is meaningful to your workflow.
+* Use slashes to separate parts of your branch names.
+* Do not use bare numbers as leading parts.
+* Avoid long descriptive names for long-lived branches.
+
+**Short well-defined tokens**
+
+Choose short tokens so they do not add too much noise to every one of your branch names.
+```
+wip       Works in progress; stuff we know won't be finished soon
+feat      Feature I'm adding or expanding
+bug       Bug fix or experiment
+junk      Throwaway branch created to experiment
+```
+
+### Linting
+
+Please be watchful of linting errors before committing code.
+
+### Commit Message Format
+
+Each commit message should include a **type**, a **scope** and a **subject**:
+
+```
+ <type>(<scope>): <subject>
+```
+
+Lines should not exceed 100 characters. This allows the message to be easier to read on github as well as in various git tools and produces a nice, neat commit log ie:
+
+```
+ #271 feat(standard): add style config and refactor to match
+ #270 fix(config): only override publicPath when served by webpack 
+ #269 feat(eslint-config-defaults): replace eslint-config-airbnb 
+ #268 feat(config): allow user to configure webpack stats output 
+``` 
+
+#### Type
+
+Must be one of the following:
+
+* **feat**: A new feature
+* **fix**: A bug fix
+* **docs**: Documentation only changes
+* **style**: Changes that do not affect the meaning of the code (white-space, formatting, missing
+  semi-colons, etc)
+* **refactor**: A code change that neither fixes a bug or adds a feature
+* **test**: Adding missing tests
+* **chore**: Changes to the build process or auxiliary tools and libraries such as documentation
+  generation
+
+#### Scope
+
+The scope could be anything specifying place of the commit change. For example `webpack`,
+`babel`, `redux` etc...
+
+#### Subject
+
+The subject contains succinct description of the change:
+
+* use the imperative, present tense: "change" not "changed" nor "changes"
+* don't capitalize first letter
+* no dot (.) at the end