Add installation and quickstart to docs start page

docs/source/index.rst

@@ -6,6 +6,63 @@
 Flake8: Your Tool For Style Guide Enforcement
 =============================================
 
+Installation
+------------
+
+To install Flake8, open an interactive shell and run:
+
+.. code::
+
+    python<version> -m pip install flake8
+
+If you want Flake8 to be installed for your default Python installation, you
+can instead use:
+
+.. code::
+
+    python -m pip install flake8
+
+.. note::
+
+    It is **very** important to install Flake8 on the *correct* version of
+    Python for your needs. If you want Flake8 to properly parse new language
+    features in Python 3.5 (for example), you need it to be installed on 3.5
+    for those features to be understandable. In many ways, Flake8 is tied to
+    the version of Python on which it runs.
+
+Quickstart
+----------
+
+To start using Flake8, open an interactive shell and run:
+
+.. code::
+
+    flake8 path/to/code/to/check.py
+    # or
+    flake8 path/to/code/
+
+.. note::
+
+    If you have installed Flake8 on a particular version of Python (or on
+    several versions), it may be best to instead run ``python<version> -m
+    flake8``.
+
+If you only want to see the instances of a specific warning or error, you can
+*select* that error like so:
+
+.. code::
+
+    flake8 --select <Error> path/to/code/
+
+Alternatively, if you want to *ignore* only one specific warning or error:
+
+.. code::
+
+    flake8 --ignore <Error> path/to/code/
+
+Please read our user guide for more information about how to use and configure
+Flake8.
+
 User Guide
 ----------