chore: added more docs/examples to with_user_session_token (#379)

Added a couple more examples to make it clearer to people using the SDK
how this function works to generate a visitor client.

src/posit/connect/client.py

@@ -182,6 +182,11 @@ def with_user_session_token(self, token: str) -> Client:
         a user session token will not exist, which will cause this method to result in an error needing
         to be handled in your application.
 
+        Depending on the type of application you are building, the user session token is retrieved in
+        a variety of ways. For example, in Streamlit and Shiny applications, the token is stored in the
+        context or session object headers using the `Posit-Connect-User-Session-Token` key. For API
+        applications, the token is added to the request headers.
+
         Parameters
         ----------
         token : str
@@ -192,10 +197,56 @@ def with_user_session_token(self, token: str) -> Client:
         Client
             A new Client instance authenticated with an API key exchanged for the user session token.
 
+        Raises
+        ------
+        ValueError
+            If the provided token is `None` or empty or if the exchange response is malformed.
+        ClientError
+            If the token exchange request with the Connect Server fails.
+
         Examples
         --------
-        >>> from posit.connect import Client
-        >>> client = Client().with_user_session_token("my-user-session-token")
+        ```python
+        from posit.connect import Client
+        client = Client().with_user_session_token("my-user-session-token")
+        ```
+
+        Example using user session token from Shiny session:
+        ```python
+        from posit.connect import Client
+        from shiny.express import render, session
+
+        client = Client()
+
+        @reactive.calc
+        def visitor_client():
+            ## read the user session token and generate a new client
+            user_session_token = session.http_conn.headers.get(
+                "Posit-Connect-User-Session-Token"
+            )
+            return client.with_user_session_token(user_session_token)
+        @render.text
+        def user_profile():
+            # fetch the viewer's profile information
+            return visitor_client().me
+        ```
+
+        Example of when the visitor's token could not be retrieved (for
+        example, if this app allows unauthenticated access) and handle
+        that in cases where a token is expected.
+        ```python
+        from posit.connect import Client
+        import requests
+
+        # Simulate request without header
+        mock_request = requests.Request()
+        visitor_client = None
+        token = request.headers.get("Posit-Connect-User-Session-Token")
+        if token:
+            visitor_client = Client().with_user_session_token(token)
+        else:
+            print("This app requires a user session token to operate.")
+        ```
         """
         if token is None or token == "":
             raise ValueError("token must be set to non-empty string.")