Update readme (#536)

### What

There's a new template in town. Let's update the readme.

Author: Gil Mizrahi

docs/architecture.md

@@ -5,7 +5,7 @@
 The query engine's job is to take a `QueryRequest`, which contains information about the query a user would like to run,
 translate it to PostgreSQL SQL, execute it against the database, and return the results as a `QueryResponse`.
 
-One place in particular that uses the Query Engine is the `/query` endpoint (defined in the `ndc-hub` repository).
+One place in particular that uses the Query Engine is the `/query` endpoint (defined in the `ndc-sdk-rs` repository).
 
 `/query` endpoints receives a `QueryRequest`, and calls the `translate` function from the Query Engine
 with it and with the information about the tables tracked in the metadata to receive and `ExecutionPlan`.
@@ -65,9 +65,9 @@ pub struct ExecutionPlan<Query> {
 /// The query we want to run with some additional information.
 pub struct Query {
     /// The root field name of the top-most collection.
-    pub root_field: String,
+    pub root_field: CollectionName,
     /// foreach variables.
-    pub variables: Option<Vec<BTreeMap<String, serde_json::Value>>>,
+    pub variables: Option<Vec<BTreeMap<ArgumentName, serde_json::Value>>>,
     /// The query.
     pub query: sql::ast::Select,
 }

docs/readme.md

@@ -2,7 +2,6 @@
 
 `ndc-postgres` is a [Hasura](https://hasura.io/) connector for PostgreSQL.
 
-- [Usage](./usage.md)
 - [Architecture](./architecture.md)
 - [Code of Conduct](./code-of-conduct.md)
 - [Debugging](./debugging.md)

docs/usage.md

@@ -10,12 +10,38 @@
 The Hasura PostgreSQL Connector allows for connecting to a PostgreSQL database giving you an instant
 GraphQL API on top of your PostgreSQL data.
 
-This connector is built using the [Rust Data Connector SDK](https://github.com/hasura/ndc-hub#rust-sdk)
+This connector is built using the [Rust Data Connector SDK](https://github.com/hasura/ndc-sdk-rs)
 and implements the [Data Connector Spec](https://github.com/hasura/ndc-spec).
 
 - [Connector information in the Hasura Hub](https://hasura.io/connectors/postgres)
 - [Hasura V3 Documentation](https://hasura.io/docs/3.0)
 
+## Features
+
+Below, you'll find a matrix of all supported features for the PostgreSQL connector:
+
+| Feature                | Supported |
+| ---------------------- | --------- |
+| Native Queries         | ✅        |
+| Native Mutations       | ✅        |
+| Simple Object Query    | ✅        |
+| Filter / Search        | ✅        |
+| Simple Aggregation     | ✅        |
+| Sort                   | ✅        |
+| Paginate               | ✅        |
+| Table Relationships    | ✅        |
+| Views                  | ✅        |
+| Mutations              | ✅        |
+| Distinct               | ✅        |
+| Enums                  | ✅        |
+| Default Values         | ✅        |
+| User-defined Functions | ❌        |
+
+## Using the PostgreSQL connector
+
+Hasura DDN's [Getting Started](https://hasura.io/docs/3.0/getting-started/build/connect-to-data/connect-a-source?db=PostgreSQL)
+guide contains information about how to use the PostgreSQL connector as part of a Hasura DDN project.
+
 ## Support & Troubleshooting
 
 The documentation and community will help you troubleshoot most issues.