docs: mention how to disable timeout for page.pdf() (#9167)

**What kind of change does this PR introduce?**

Add how to disable timeout for `page.pdf()`.

**Summary**

This was mentioned in the PR that adding this feature
https://github.com/puppeteer/puppeteer/pull/7508 But it has lost at
https://github.com/puppeteer/puppeteer/pull/8593.

I'm not sure why this was removed, but I think this info is useful for
users.

**Does this PR introduce a breaking change?**

no

packages/puppeteer-core/src/common/PDFOptions.ts

@@ -167,7 +167,7 @@ export interface PDFOptions {
    */
   omitBackground?: boolean;
   /**
-   * Timeout in milliseconds
+   * Timeout in milliseconds. Pass `0` to disable timeout.
    * @defaultValue 30000
    */
   timeout?: number;