Docs: add timeout example

lib/output.js

@@ -1050,6 +1050,17 @@ function tile (options) {
  * The clock starts when libvips opens an input image for processing.
  * Time spent waiting for a libuv thread to become available is not included.
  *
+ * @example
+ * // Ensure processing takes no longer than 3 seconds
+ * try {
+ *   const data = await sharp(input)
+ *     .blur(1000)
+ *     .timeout({ seconds: 3 })
+ *     .toBuffer();
+ * } catch (err) {
+ *   if (err.message.includes('timeout')) { ... }
+ * }
+ *
  * @since 0.29.2
  *
  * @param {Object} options