docs: Add README of flask example.

Author: abawchen

examples/flask_mongoengine/README.md

@@ -0,0 +1,51 @@
+
+Example Flask+MongoEngine Project
+================================
+
+This example project demos integration between Graphene, Flask and MongoEngine.
+The project contains two models, one named `Department` and another
+named `Employee`.
+
+Getting started
+---------------
+
+First you'll need to get the source of the project. Do this by cloning the
+whole Graphene repository:
+
+```bash
+# Get the example project code
+git clone [email protected]:abawchen/graphene-mongo.git
+cd graphene-mongo/examples/flask_mongoengine
+```
+
+It is good idea (but not required) to create a virtual environment
+for this project. We'll do this using
+[virtualenv](http://docs.python-guide.org/en/latest/dev/virtualenvs/)
+to keep things simple,
+but you may also find something like
+[virtualenvwrapper](https://virtualenvwrapper.readthedocs.org/en/latest/)
+to be useful:
+
+```bash
+# Create a virtualenv in which we can install the dependencies
+virtualenv env
+source env/bin/activate
+```
+
+Now we can install our dependencies:
+
+```bash
+pip install -r requirements.txt
+```
+
+Now the following command will setup the database, and start the server:
+
+```bash
+./app.py
+
+```
+
+
+Now head on over to
+[http://127.0.0.1:5000/graphql](http://127.0.0.1:5000/graphql)
+and run some queries!