Updated test cases documentation

docs/test_cases/t20002.md

@@ -0,0 +1,42 @@
+# t20002 - Free function sequence diagram test case
+## Config
+```yaml
+compilation_database_dir: ..
+output_directory: puml
+diagrams:
+  t20002_sequence:
+    type: sequence
+    glob:
+      - ../../tests/t20002/t20002.cc
+    include:
+      namespaces:
+        - clanguml::t20002
+    using_namespace:
+      - clanguml::t20002
+    start_from:
+      - function: "clanguml::t20002::m1()"
+
+```
+## Source code
+File t20002.cc
+```cpp
+#include <algorithm>
+#include <numeric>
+#include <vector>
+
+namespace clanguml {
+namespace t20002 {
+
+void m4() { }
+
+void m3() { m4(); }
+
+void m2() { m3(); }
+
+void m1() { m2(); }
+}
+}
+
+```
+## Generated UML diagrams
+![t20002_sequence](./t20002_sequence.png "Free function sequence diagram test case")