docs(README): add example usage for new MBQL sub-package

Signed-off-by: Charles Lariviere <charles@dribbble.com>

Author: Charles Lariviere

README.md

@@ -90,10 +90,11 @@ for user in User.list():
     )
 ```
 
-You can also execute queries and get results back as a Pandas DataFrame. Currently, you need to provide
-the exact MBQL (i.e. Metabase Query Language) as the `query` argument.
+You can also execute queries and get results back as a Pandas DataFrame. You can provide the exact MBQL, or use
+the `Query` object to compile MBQL (i.e. Metabase Query Language) from Python classes included in this package.
+
 ```python
-from metabase import Dataset
+from metabase import Dataset, Query, Count, GroupBy, TemporalOption
 
 dataset = Dataset.create(
     using.metabase,
@@ -106,9 +107,76 @@ dataset = Dataset.create(
     },
 )
 
+# compile the MBQL above using the Query object
+dataset = Dataset.create(
+    database=1,
+    type="query",
+    query=Query(
+        table_id=2,
+        aggregations=[Count()],
+        group_by=[GroupBy(id=7, option=TemporalOption.YEAR)]
+    ).compile(),
+)
+
 df = dataset.to_pandas()
 ```
 
+As shown above, the `Query` object allows you to easily compile MBQL from Python objects. Here is a
+more complete example:
+```python
+from metabase import Query, Sum, Average, Greater, GroupBy, BinOption, TemporalOption
+
+query = Query(
+    table_id=5,
+    aggregations=[
+        Sum(id=5),                                  # Provide the ID for the Metabase field
+        Average(id=5, name="Average of Price")      # Optionally, you can provide a name
+    ],
+    filters=[
+        Greater(id=1, value=5.5)                    # Filter for values of FieldID 1 greater than 5.5
+    ],
+    group_by=[
+        GroupBy(id=4),                              # Group by FieldID 4
+        GroupBy(id=5, option=BinOption.AUTO),       # You can use Metabase's binning feature for numeric fields
+        GroupBy(id=5, option=TemporalOption.YEAR)   # Or it's temporal option for date fields
+    ]
+)
+
+print(query.compile())
+{
+    'source-table': 5,
+    'aggregation': [
+        ['sum', ['field', 5, None]],
+        ['aggregation-options', ['avg', ['field', 5, None]], {'name': 'Average of Price', 'display-name': 'Average of Price'}]
+    ],
+    'breakout': [
+        ['field', 4, None],
+        ['field', 5, {'binning': {'strategy': 'default'}}],
+        ['field', 5, {'temporal-unit': 'year'}]
+    ],
+    'filter': ['>', ['field', 1, None], 5.5]
+}
+```
+
+This can also be used to more easily create `Metric` objects.
+
+```python
+from metabase import Metric, Query, Count, EndsWith, CaseOption
+
+
+metric = Metric.create(
+    name="Gmail Users",
+    description="Number of users with a @gmail.com email address.",
+    table_id=2,
+    definition=Query(
+        table_id=1,
+        aggregations=[Count()],
+        filters=[EndsWith(id=4, value="@gmail.com", option=CaseOption.CASE_INSENSITIVE)]
+    ).compile()
+)
+```
+
+
 
 ## Endpoints