add FAQ (Qiskit/qiskit-metapackage#219)

* fixes Qiskit/qiskit-metapackage#113

* added link to install instructions

fixed some styles

* Review changes

- Add Q&A Format

qiskit-docs/faq.rst

@@ -0,0 +1,89 @@
+==========================
+Frequently Asked Questions
+==========================
+
+**Q: How should I cite Qiskit in my research?**
+
+**A:** Please cite Qiskit by using the included `BibTeX file
+<https://raw.githubusercontent.com/Qiskit/qiskit/master/Qiskit.bib>`_.
+
+|
+
+**Q: Why do I receive the error message** ``AttributeError: 'str' object has no
+attribute 'configuration'`` **when I try to execute or compile a circuit on a
+backend?**
+
+**A:** The backend parameter of these two functions takes in a ``BaseBackend`` type,
+which can be returned by calling one of these methods, one for simulators and one
+for real quantum devices.
+
+* For simulators:
+
+.. code:: python
+
+  Aer.get_backend('<backend_name>')
+
+* For real devices:
+
+.. code:: python
+
+  IBMQ.get_backend('<backend_name>')
+
+For example, if you want to run a job on the ``'ibmqx4'`` backend, the
+following code would throw the error message:
+
+.. code:: python
+
+  job = execute(circuit, backend='ibmqx4', shots=100)
+
+Instead, the code should be written as
+
+.. code:: python
+
+  my_backend = IBMQ.get_backend('ibmqx4')
+  job = execute(circuit, backend=my_backend, shots=100)
+
+|
+
+**Q: Why do I receive the error message** ``Error: Instance of QuantumCircuit has no
+member`` **when adding gates to a circuit?**
+
+**A:** This is a pylint error, which is a Linter for Python. Linters analyze
+code for potential errors, and they throw errors when they find
+potentially erroneous code. However, this error should not prevent your
+code from compiling or running, so there is no need to worry. The error
+message can be disabled by adding the following line above the code that
+is causing the error:
+
+.. code:: python
+
+  #pylint: disable=no-member
+
+|
+
+**Q: Why do my results from real devices differ from my results from the simulator?**
+
+**A:** The simulator runs jobs as though is was in an ideal environment; one
+without noise or decoherence. However, when jobs are run on the real devices
+there is noise from the environment and decoherence, which causes the qubits
+to behave differently than what is intended.
+
+|
+
+**Q: Why do I receive the error message,** ``No Module 'qiskit'`` **when using Jupyter Notebook?**
+
+**A:** If you used ``pip install qiskit`` and set up your virtual environment in
+Anaconda, then you may experience this error when you run a tutorial
+in Jupyter Notebook. If you have not installed Qiskit or set up your
+virtual environment, you can follow the
+`installation steps <https://qiskit.org/documentation/install.html#install>`__.
+
+The error is caused when trying to import the Qiskit package in an
+environment where Qiskit is not installed. If you launched Jupyter Notebook
+from the Anaconda-Navigator, it is possible that Jupyter Notebook is running
+in the base (root) environment, instead of in your virtual
+environment. Choose a virtual environment in the Anaconda-Navigator from the
+**Applications on** dropdown menu. In this menu, you can see
+see all of the virtual environments within Anaconda, and you can
+select the environment where you have Qiskit installed to launch Jupyter
+Notebook.