Update example README.md

Update example README.md to use the correct markdown syntax for links.

Author: roaldnefs

examples/prometheus/README.md

@@ -5,8 +5,8 @@ To run a demo Prometheus, you'll need to follow these steps:
 * Have a Django application running and exporting its stats. The
   provided `prometheus.yml` assumes the stats are exported at
   `http://127.0.0.1:8000/metrics`.
-* Install Prometheus by cloning it somewhere, see the (installation
-  instructions)[http://prometheus.io/docs/introduction/install/].
+* Install Prometheus by cloning it somewhere, see the [installation
+  instructions](http://prometheus.io/docs/introduction/install/).
   Let's assume you cloned it to `~/prometheus`.
 * Run prometheus like this:
   ```shell