Add test documentation to README (#181)

* Add test documentation to README

* Add notice/warning

* PR feedback -- generalize mongoDB setup

Author: kyeah

README.md

@@ -112,3 +112,41 @@ fn main() {
     ...
 }
 ```
+
+Testing
+-------
+
+The driver test suite is largely composed of integration tests and behavioral unit-tests, relying on the official [MongoDB specifications repo](https://github.com/mongodb/specifications). 
+
+The easiest way to thoroughly test the driver is to set your fork up with TravisCI. However, if you'd rather test the driver locally, you'll need to setup integration and specification tests.
+
+> NOTE: Each integration test uses a unique database/collection to allow tests to be parallelized, and will drop their dependencies before running. However, effects are _not_ cleaned up afterwards.
+
+#### Setting up integration tests
+
+All integration tests run on the default MongoDB port, 27017. Before running the tests, ensure that a test database is setup to listen on that port.
+
+If you don't have mongodb installed, download and install a version from [the MongoDB Download Center](https://www.mongodb.com/download-center). You can see a full list of versions being tested on Travis in [the travis config](/.travis.yml).
+
+After installation, run a MongoDB server on 27017:
+
+```
+mkdir -p ./data/test_db
+mongod --dbpath ./data/test_db
+```
+
+#### Setting up the specifications submodule
+
+Pull in the specifications submodule at `tests/json/data/specs`.
+
+```
+git submodule update --init
+```
+
+#### Running Tests
+
+Run tests like a regular Rust program:
+
+```
+cargo test --verbose
+```