[doc][core] A quick documentation is added for declaring tasks as non-critical tasks.

Author: claireguyot

docs/handbook/configuration.md

@@ -1 +1,17 @@
-# Workflow and Task Configuration
+# Workflow and Task Configuration
+
+## Non-critical tasks
+
+Any task in a workflow can be declared as non-critical. A non-critical task is a task that doesn't trigger a global environment ERROR in case of failure. The state of a non-critical task doesn't affect the environment state in any way.
+
+To declare a task as non-critical, a line has to be added in the corresponding workflow template. Under the task role, in the `task` section (usually after the `load` statement), the line to add is `critical: false`, like in the following example:
+
+```yaml
+roles:
+  - name: "non-critical-task"
+    vars:
+      non-critical-task-var: 'var-value'
+    task:
+      load: mytask
+      critical: false
+```