Update readme (#17)

Updated readme so it has a tutorial and more full description of what this package does

Author: juliusgeo

README.rst

@@ -1,2 +1,68 @@
-This package provides an ExplainCollection class
-that allows common MongoDB commands to be explained
+This package provides an ``ExplainCollection`` class
+that allows that allows PyMongo's Collection methods to be explained_
+
+.. _explained: https://docs.mongodb.com/master/reference/command/explain/#dbcmd.explain.
+
+
+Tutorial
+########
+
+PyMongo operations in existing application code can be explained by swapping ``Collection`` objects with ``ExplainCollection``
+objects. The ``ExplainCollection`` class provides all CRUD API methods provided by PyMongo's ``Collection``,
+but using this class to run operations runs explain on them, instead of executing them.
+
+To run explain on a command, first instantiate an ``ExplainCollection`` from the ``Collection`` object originally used to run the command::
+
+    collection = client.db.products
+    explain = ExplainCollection(collection)
+
+Now you are ready to explain some commands. Remember that explaining a command does not execute it::
+
+    result = explain.update_one({"quantity": 1057, "category": "apparel"}, {"$set": {"reorder": True}})
+
+Now ``result`` will contain the output of running explain on the given ``update_one`` command::
+
+    {'$clusterTime':
+        {'signature': {
+            'keyId': 0, 'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'},
+            'clusterTime': Timestamp(1595603051, 3)},
+            'serverInfo': {'host': 'Juliuss-MBP.verizon.net', 'version': '4.4.0-rc13', 'port': 27017, 'gitVersion': '27f5c1ee9f513f29fe30b8ebefed99581428c6e1'},
+            'queryPlanner':
+                {'plannerVersion': 1,
+                'queryHash': 'CD8F6D8F',
+                'parsedQuery':
+                    {'$and': [
+                    {'category': {'$eq': 'apparel'}},
+                    {'quantity': {'$eq': 1057}}]},
+                    'namespace': 'db.products',
+                    'indexFilterSet': False,
+                    'winningPlan':
+                    {'inputStage':
+                        {'filter':
+                            {'$and': [
+                                {'category': {'$eq': 'apparel'}},
+                      {'quantity': {'$eq': 1057}}]},
+                       'stage': 'COLLSCAN', 'direction': 'forward'},
+                       'stage': 'UPDATE'}, 'planCacheKey': 'CD8F6D8F',
+                      'rejectedPlans': []}, 'ok': 1.0,
+                      'operationTime': Timestamp(1595603051, 3)}
+
+
+Since ``ExplainCollection`` instances provide all the same methods provided by ``Collection`` instances, explaining operations in your application code is a simple matter of replacing ``Collection`` instances in your application code with ``ExplainCollection`` instances.
+
+
+Explaining commands in a script
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+You can also run explain on all commands within a Python script using our CLI tool.
+Given a script that contains ``pymongo`` commands within it, you can simply run: ::
+
+    python3 -m pymongoexplain <path/to/your/script.py>
+
+This will print out the explain output for every single command
+within that script, in addition to running the script itself.
+
+Any positional parameters or arguments required by your script can be
+simply be appended to the invocation as follows::
+
+    python3 -m pymongoexplain <path/to/your/script.py> [PARAMS] [--optname OPTS]