fix: Update README partials to mention how to use import (#1400)

* Update READM partials to mention how to use import

GitHub issue #1398 indicates that a specific incantation is required when using "import" with the trace-agent. This PR updates the README to mention this.

* 🦉 Updates from OwlBot

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: dnoe

.readme-partials.yaml

@@ -18,6 +18,12 @@ body: |-
     require('@google-cloud/trace-agent').start();
     // ...
     ```
+    
+    If you want to use `import`, you will need to do the following to import all required types:
+
+    ```
+    import * as TraceAgent from '@google-cloud/trace-agent';
+    ```
 
     Optionally, you can pass a [configuration object](https://github.com/googleapis/cloud-trace-nodejs/blob/master/src/config.ts) to the `start()` function as follows:
 

README.md

@@ -73,6 +73,12 @@ require('@google-cloud/trace-agent').start();
 // ...
 ```
 
+If you want to use `import`, you will need to do the following to import all required types:
+
+```
+import * as TraceAgent from '@google-cloud/trace-agent';
+```
+
 Optionally, you can pass a [configuration object](https://github.com/googleapis/cloud-trace-nodejs/blob/master/src/config.ts) to the `start()` function as follows:
 
 <!-- TODO(kjin): Generate documentation from the public interface of the Trace Agent, and link it here. -->