Update README

Author: christippett

README.md

@@ -1,18 +1,86 @@
 # BigQuery View Analyzer
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 ## Description
-TBC
+`bigquery-view-analyzer` is a command-line tool for visualizing dependencies and managing permissions between BigQuery views.
+
+To authorize a vew, permissions must be granted at a dataset level for every view/table referenced in the view definition. This requirement cascades down to every view that's referenced by the parent view, they too must have permissions granted for every view/table they reference - and so on. This can quickly become difficult to manage if you have many nested views across multiple datasets and/or projects.
+
+`bigquery-view-analyzer` automatically resolves these dependencies and applies the relevant permissions to all views and datasets referenced by the parent view.
+
 
 ## Installation
 
 ```bash
-pip install bigquery-view-analyzer
+$ pip install bigquery-view-analyzer
 ```
 
 ## Usage
-TBC
+
+```bash
+$ bqva --help
+```
+
+
+### Example
+
+![Example tree](/docs/example.png)
+
+Given the above datasets and tables in BigQuery, to authorize `bqva-demo:dataset_4.shared_view`, the following views would need to be authorized with each of the following datasets:
+
+- Authorized views for **`dataset_1`**
+    - `bqva-demo:dataset_3.view_a_b_c_d`
+- Authorized views for **`dataset_2`**
+    - `bqva-demo:dataset_3.view_a_b_c_d`
+    - `bqva-demo:dataset_1.view_c`
+- Authorized views for **`dataset_3`**
+    - `bqva-demo:dataset_2.view_d`
+    - `bqva-demo:dataset_4.shared_view`
+
+You can easily visualize the above view hierarchy using the `bqva tree` command.
+
+```bash
+# View dependency tree and authorization status for 'bqva-demo:dataset_4.shared_view'
+$ bqva tree --status --view "bqva-demo:dataset_4.shared_view"
+bqva-demo:dataset_4.shared_view
+└── bqva-demo:dataset_3.view_a_b_c_d (⨯)
+    ├── bqva-demo:dataset_1.table_a (⨯)
+    ├── bqva-demo:dataset_1.table_b (⨯)
+    ├── bqva-demo:dataset_1.view_c (⨯)
+    │   └── bqva-demo:dataset_2.table_c (⨯)
+    └── bqva-demo:dataset_2.view_d (⨯)
+        └── bqva-demo:dataset_3.table_d (⨯)
+```
+
+Permissions can be applied automatically to all datasets referenced by the parent view using the `bqva authorize` command.
+
+```bash
+# Apply all permissions required by 'bqva-demo:dataset_4.shared_view'
+$ bqva authorize --view "bqva-demo:dataset_4.shared_view"
+bqva-demo:dataset_4.shared_view
+└── bqva-demo:dataset_3.view_a_b_c_d (✓)
+    ├── bqva-demo:dataset_1.table_a (✓)
+    ├── bqva-demo:dataset_1.table_b (✓)
+    ├── bqva-demo:dataset_1.view_c (✓)
+    │   └── bqva-demo:dataset_2.table_c (✓)
+    └── bqva-demo:dataset_2.view_d (✓)
+        └── bqva-demo:dataset_3.table_d (✓)
+```
+
+If you want to revoke permissions for a view, you can do that too!
+
+```bash
+# Revoke all permissions granted to 'bqva-demo:dataset_4.shared_view'
+$ bqva revoke --view "bqva-demo:dataset_4.shared_view"
+bqva-demo:dataset_4.shared_view
+└── bqva-demo:dataset_3.view_a_b_c_d (⨯)
+    ├── bqva-demo:dataset_1.table_a (⨯)
+    ├── bqva-demo:dataset_1.table_b (⨯)
+    ├── bqva-demo:dataset_1.view_c (⨯)
+    │   └── bqva-demo:dataset_2.table_c (⨯)
+    └── bqva-demo:dataset_2.view_d (⨯)
+        └── bqva-demo:dataset_3.table_d (⨯)
+```