Move CONTRIBUTING.md to top level (Qiskit#314)

* Move CONTRIBUTING.md to top level

The CONTRIBUTING.md doc contains a lot of useful information about the
not only contributing to the project but also some useful information
about project policy and conventions. But it's currently in a hidden
directory so that github ui will show it on a help menu. So unless you
know to click on that help menu or that it's hiding in the .github
directory you'll never see it. This commit addresses this by moving the
file to the repo root so it's more obvious where it is.

Mirror of Qiskit/qiskit#2359 Qiskit/qiskit-aer#229
qiskit-community/qiskit-ignis#216 qiskit-community/qiskit-aqua#556
Qiskit/qiskit-ibmq-provider#149 and Qiskit/qiskit-chemistry#163

* Move code of conduct and switch CHANGELOG to markdown

* Update changelog title formatting

CHANGELOG.md

@@ -0,0 +1,128 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a
+Changelog](http://keepachangelog.com/en/1.0.0/).
+
+> **Types of changes:**
+>
+> -   **Added**: for new features.
+> -   **Changed**: for changes in existing functionality.
+> -   **Deprecated**: for soon-to-be removed features.
+> -   **Removed**: for now removed features.
+> -   **Fixed**: for any bug fixes.
+> -   **Security**: in case of vulnerabilities.
+
+[UNRELEASED](https://github.com/Qiskit/qiskit-terra/compare/0.10.3...HEAD)
+==========================================================================
+
+[0.10.3](https://github.com/Qiskit/qiskit/compare/0.10.2...0.10.3) - 2019-05-29
+===============================================================================
+
+Changed
+-------
+
+-   Increased the qiskit-terra version the latest release 0.8.1 (\#309)
+
+[0.10.2](https://github.com/Qiskit/qiskit/compare/0.10.1...0.10.2) - 2019-05-24
+===============================================================================
+
+Changed
+-------
+
+-   Updated `qiskit-aer` dependency to 0.2.1. (\#302)
+-   Increased the qiskit-aqua version the latest release 0.5.1, this
+    removes torch as a mandatory requirement. (\#303)
+
+[0.10.1](https://github.com/Qiskit/qiskit/compare/0.10.0...0.10.1) - 2019-05-07
+===============================================================================
+
+Changed
+-------
+
+-   Updated the `qiskit-ibmq-provider` dependency to 0.2.2.
+
+[0.10.0](https://github.com/Qiskit/qiskit/compare/0.9.0...0.10.0) - 2019-05-06
+==============================================================================
+
+Changed
+-------
+
+-   Updated the `qiskit-ibmq-provider` dependency to 0.2.1 (\#244).
+
+[0.9.0](https://github.com/Qiskit/qiskit/compare/0.8.1...0.9.0) - 2019-05-02
+============================================================================
+
+Added
+-----
+
+-   Added the qiskit-ibmq-provider package to the metapackage (\#227).
+-   Added qiskit-aqua and qiskit-chemistry to the set of installed
+    packages (\#185)
+
+Changed
+-------
+
+-   The qiskit-terra version increased to the next feature release 0.8.0
+    (\#227).
+-   The qiskit-aer version increased to the next feature release 0.2.0
+    (\#227).
+-   The qiskit-ignis version increased to the next release 0.1.1
+    (\#227).
+
+[0.8.1](https://github.com/Qiskit/qiskit/compare/0.8.0...0.8.1) - 2019-05-01
+============================================================================
+
+Changed
+-------
+
+-   Increased the qiskit-terra version to v0.7.2 which includes a fix
+    for the schema validation of backend configuration in
+    Qiskit/qiskit-terra\#2258 (\#217)
+
+[0.8.0](https://github.com/Qiskit/qiskit/compare/0.7.3...0.8.0) - 2019-03-05
+============================================================================
+
+Added
+-----
+
+-   Added qiskit-ignis to the set of installed packages (\#164)
+
+Changed
+-------
+
+-   Increased the qiskit-terra version to v0.7.1 which includes a fix
+    for the BasicAer simulator issue documented in
+    Qiskit/qiskit-terra\#1583 and Qiskit/qiskit-terra\#1838 (\#167).
+
+[0.7.3](https://github.com/Qiskit/qiskit/compare/0.7.2...0.7.3) - 2019-02-20
+============================================================================
+
+Fixed
+-----
+
+-   Added a workaround for installing package when using pip 19.0.2
+    (\#119)
+
+[0.7.2](https://github.com/Qiskit/qiskit/compare/0.7.1...0.7.2) - 2019-01-23
+============================================================================
+
+Fixed
+-----
+
+-   Fixed upgrading to 0.7.x when wheel is present (\#45)
+
+[0.7.1](https://github.com/Qiskit/qiskit/compare/0.7.0...0.7.1) - 2019-01-17
+============================================================================
+
+-   Fixed an issue when upgrading from an older `qiskit` package to a
+    version [\>=0.7.0]{.title-ref} (\#32)
+
+0.7.0 - 2018-12-19
+==================
+
+Added
+-----
+
+-   First release, includes qiskit-terra and qiskit-aer