Updated test case documentation

docs/test_cases/t20007.md

@@ -0,0 +1,49 @@
+# t20007 - Class template variadic argument list sequence diagram
+## Config
+```yaml
+compilation_database_dir: ..
+output_directory: puml
+diagrams:
+  t20007_sequence:
+    type: sequence
+    glob:
+      - ../../tests/t20007/t20007.cc
+    include:
+      namespaces:
+        - clanguml::t20007
+    using_namespace:
+      - clanguml::t20007
+    start_from:
+      - function: "clanguml::t20007::tmain()"
+```
+## Source code
+File t20007.cc
+```cpp
+#include <string>
+#include <utility>
+
+namespace clanguml {
+namespace t20007 {
+
+template <typename First, typename... Args> struct Adder {
+    First add(First &&arg, Args &&...args) { return (arg + ... + args); }
+};
+
+void tmain()
+{
+    using namespace std::string_literals;
+
+    Adder<int, int> adder1;
+    Adder<int, float, double> adder2;
+    Adder<std::string, std::string, std::string> adder3;
+
+    [[maybe_unused]] auto res1 = adder1.add(2, 2);
+    [[maybe_unused]] auto res2 = adder2.add(1, 2.0, 3.0);
+    [[maybe_unused]] auto res3 = adder3.add("one"s, "two"s, "three"s);
+}
+
+}
+}
+```
+## Generated UML diagrams
+![t20007_sequence](./t20007_sequence.svg "Class template variadic argument list sequence diagram")