Doc: targetting specific runner doc

README.md

@@ -587,7 +587,7 @@ I.e:
 * `cluster:okd-c1` 
 * `type:groups` 
 * `instance:technologie.cbi.grac`
-* `ctx:releng-group` 
+* `ctx:medium` 
 * `executor:kubernetes` 
 * `kubenamespace:ef-grac-technologie-cbi-grac`
 * `concurrent:8` 
@@ -630,6 +630,16 @@ my_job:
     - echo "Running on a Eclipse foundation runner"
 ```
 
+Q: **How do I choose the type of runner in a job?**
+
+```yaml
+my_job:
+  tags:
+    - ctx:medium
+  script:
+    - echo "Running on a Eclipse foundation runner of medium type"
+```
+
 Q: **What if no runner matches the specified tags?**
 
 A: If no runner matches the specified tags, the job won't run. Make sure that your runner tags correspond to the capabilities of your runners and the requirements of your jobs.