Added jinja template documentation example

docs/configuration_file.md

@@ -60,6 +60,68 @@ The following, are the `clang-uml` additional template functions:
 * `alias(string)` - returns a PlantUML alias of an C++ entity represented by string name
 * `comment(string)` - returns a comment of an C++ entity represented by string name
 
+Templates allow complex postprocessing of the diagrams, for instance creation of customized PlantUML
+notes in the diagrams from comments in the code. Below is an example of using the above commands to
+generate notes in the PlantUML diagram from code comments (see also test case [t00050](./test_cases/t00050.md)):
+
+```yaml
+    plantuml:
+      after:
+        # Add a note left of the `A` class with the entire clas comment as content
+        - >
+           note left of {{ alias("A") }}
+              {{ comment("clanguml::t00050::A").formatted }}
+           end note
+        # Same as above
+        - >
+          note right of {{ element("clanguml::t00050::A").alias }}
+             {% set e=element("clanguml::t00050::A") %} {{ e.comment.formatted }}
+          end note
+        # Add a note left of class 'C' using trimmed text content from the class comment
+        - >
+          note left of {{ alias("C") }} #AABBCC
+             {{ trim(comment("clanguml::t00050::C").text) }}
+          end note
+        # For each element in the diagram (class, template, enum):
+        #  - Add a note with \brief comment if exists
+        #  - Add a note with \todo for each element which has it
+        #  - Add a note with template parameter descriptions based on \tparam comment
+        - >
+          {# Render brief comments and todos, if any were written for an element #}
+          {% for e in diagram.elements %}
+          {% if existsIn(e, "comment") and existsIn(e.comment, "brief") %}
+
+          note top of {{ e.alias }} {% if e.type == "class" %} #22AA22 {% else %} #2222AA {% endif %}
+             {% set c=e.comment %} {{ c.brief.0 }}
+          end note
+
+          {% endif %}
+          {% if existsIn(e, "comment") and existsIn(e.comment, "todo") %}
+          {% set c=e.comment %}
+          {% for t in c.todo %}
+          note top of {{ e.alias }} #882222
+             **TODO**
+             {{ t }}
+          end note
+
+          {% endfor %}
+
+          {% endif %}
+          {# Render template paramete if any #}
+          {% if existsIn(e, "comment") and existsIn(e.comment, "tparam") %}
+          {% set c=e.comment %}
+
+          note top of {{ e.alias }} #AAAAFF
+             **Template parameters**
+             {% for tp in c.tparam %}
+             //{{ tp.name }}// {{ trim(tp.description) }}
+             {% endfor %}
+          end note
+
+          {% endif %}
+          {% endfor %}
+```
+
 ## Example complete config
 
 ```yaml