Updated test case documentation

docs/test_cases/t20019.md

@@ -0,0 +1,58 @@
+# t20019 - Curiously Recurring Template Pattern sequence diagram test case
+## Config
+```yaml
+compilation_database_dir: ..
+output_directory: puml
+diagrams:
+  t20019_sequence:
+    type: sequence
+    glob:
+      - ../../tests/t20019/t20019.cc
+    include:
+      namespaces:
+        - clanguml::t20019
+    using_namespace:
+      - clanguml::t20019
+    start_from:
+      - function: "clanguml::t20019::tmain()"
+```
+## Source code
+File t20019.cc
+```cpp
+#include <cstdio>
+
+namespace clanguml {
+namespace t20019 {
+
+// From https://en.cppreference.com/w/cpp/language/crtp
+
+template <class Derived> struct Base {
+    void name() { (static_cast<Derived *>(this))->impl(); }
+};
+
+struct D1 : public Base<D1> {
+    void impl() { std::puts("D1::impl()"); }
+};
+
+struct D2 : public Base<D2> {
+    void impl() { std::puts("D2::impl()"); }
+};
+
+void tmain()
+{
+    Base<D1> b1;
+    b1.name();
+    Base<D2> b2;
+    b2.name();
+
+    D1 d1;
+    d1.name();
+    D2 d2;
+    d2.name();
+}
+
+}
+}
+```
+## Generated UML diagrams
+![t20019_sequence](./t20019_sequence.svg "Curiously Recurring Template Pattern sequence diagram test case")