[pg_session_jwt] Improves the README's top level description (#12)

CC @conradludgate @bgrenon

README.md

@@ -1,17 +1,19 @@
 pg\_session\_jwt
 ================
 
-`pg_session_jwt` is a PostgreSQL extension designed to handle JSON Web Tokens (JWT) within PostgreSQL sessions. It provides utilities to manage JWT-based authentication and user sessions securely in the database.
+`pg_session_jwt` is a PostgreSQL extension designed to handle authenticated sessions through a JWT. This JWT is then verified against a JWK (JSON Web Key) to ensure its authenticity. Both the JWK and the JWT must be provided to the extension by a Postgres superuser. The extension then stores the JWT in the database for later retrieval, and exposes functions to retrieve the user ID (the `sub` subject field) and other parts of the payload.
+
+The goal of this extension is to provide a secure and efficient way to manage authenticated sessions in a PostgreSQL database. The JWTs can be generated by third-party auth providers, and then developers can leverage the JWT for [Row Level Security](https://www.postgresql.org/docs/current/ddl-rowsecurity.html) (RLS) policies, or to retrieve the user ID for other purposes (column defaults, filters, etc.).
 
 > [!WARNING]
 > This extension is under active development. The entire API is subject to change.
 
 Features
 --------
 
-* **Initialize JWT sessions** using a JWKS (JSON Web Key Set).
+* **Initialize JWT sessions** using a JWK (JSON Web Key).
 
-* **Retrieve the user ID** or session-related information directly from the database.
+* **Retrieve the user ID** or other session-related information directly from the database.
 
 * Simple JSONB-based storage and retrieval of session information.
 
@@ -20,9 +22,9 @@ Usage
 
 `pg_session_jwt` exposes four main functions:
 
-### 1\. auth.init(kid bigint, jwks jsonb) → void
+### 1\. auth.init(kid bigint, jwk jsonb) → void
 
-Initializes a session with a given key identifier (KID) and JWKS data in JSONB format.
+Initializes a session with a given key identifier (KID) and JWK data in JSONB format.
 
 ### 2\. auth.jwt\_session\_init(jwt text) → void