Add CONTRIBUTING.md, references #98.

.Rbuildignore

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 ^\.travis\.yml$
 ^codecov\.yml$
 ^\.github$
+^CONTRIBUTING\.md$

CONTRIBUTING.md

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+# How to contribute?
+
+This document contains guidelines for the collaboration in the **hereR** R package.
+
+## Getting started
+
+Ready to contribute? Here's how to set up **hereR** for local development.
+
+1. Fork the repository to your GitHub account and clone the forked repository locally.
+2. Install the dependencies (check the `DESCRIPTION` file).
+3. Create a feature or bugfix branch as appropriate: `git checkout -b feature/<feature-description> develop` or `git checkout -b bugfix/<bugfix-description> develop`
+4. Work locally on the feature, make sure to add or adjust:
+    - entries in NEWS.md
+    - function documentation (run `devtools::document()` before commiting)
+    - tests for the feature (run `data-raw/internal.R` to recreate package example data and API mocks)
+    - vignettes
+5. Commit and push changes to the new branch.
+6. If you are done with the new feature or bugfix and CI tests are passing on GitHub, create a pull request on GitHub of your `feature/...` or `bugfix/...` branch into the `develop` branch of the original repository (not your fork).
+
+## Gitflow workflow
+
+
+### Master and develop
+
+The [gitflow workflow](https://www.atlassian.com/git/tutorials/comparing-workflows/gitflow-workflow) uses two branches to
+record the history of the project. The `master` branch stores the official release history, and the `develop` branch serves
+as an integration branch for features. It's also convenient to tag all commits in the `master` branch with a version number.
+
+### Features
+
+Each new feature should reside in its own branch. But, instead of branching off of `master`, feature branches use
+`develop` as their parent branch. When a feature is complete, it gets merged back into `develop`. Features should never interact directly with `master`.
+
+### Release
+
+This packages uses [semantic versions](https://semver.org/). Once `develop` has aquired enough features for a release,
+fork a release (`release/v<major>.<minor>.<patch>)` branch off of `develop`. When CRAN has accepted the package submission,
+the release branch gets merged into `master` and tagged with a version number. In addition, it should be merged back into `develop`,
+which may have progressed since the release was initiated.
+
+
+## Documentation and coding style
+
+### Naming convention
+
+Use `snake_case` for variable, argument and function name definitions and avoid capital letters.
+Dots (`.`) in function definitions are reserved for the functions and method dispatch in the S3 object system (e.g. `print.my_class`) or as prefix to hide functions (e.g. `.my_hidden_function`).
+
+### Package documentation
+
+This packages uses [roxygen2](https://cran.r-project.org/web/packages/roxygen2/vignettes/roxygen2.html) for the package documentation. 
+
+Example:
+
+``` r
+#' Add together two numbers
+#'
+#' @param x A number
+#' @param y A number
+#' @return The sum of \code{x} and \code{y}
+#' @examples
+#' add(1, 1)
+#' add(10, 1)
+add <- function(x, y) {
+  x + y
+}
+```
+
+### Script header template
+
+Add a header to CLI scripts according to the following template:
+
+``` r
+#!/usr/bin/env Rscript
+# -----------------------------------------------------------------------------
+# Name          :example_script.R
+# Description   :Short description of the scripts purpose.
+# Author        :Name <your@email.ch>
+# Date          :YYYY-MM-DD
+# Version       :0.1.0
+# Usage         :./example_script.R
+# Notes         :Is there something important to consider when executing the
+#                script?
+# =============================================================================
+```
+
+## Credits
+
+Add your GitHub user name to the fixed bug or added feature entry in the `NEWS.md` to ensure credits are given correctly:
+
+```r
+# version x.x.x.9000
+
+* Added <feature description> (@<github_username>, [#1](https://github.com/munterfinger/hereR/pull/1)).
+* Bugfix: <description> (@<github_username>, closes [#2](https://github.com/munterfinger/hereR/issues/2)).
+
+```