Updated test cases documentation

docs/test_cases/t00057.md

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+# t00057 - Test case C99/C11 translation units with structs and unions
+## Config
+```yaml
+compilation_database_dir: ..
+output_directory: puml
+diagrams:
+  t00057_class:
+    type: class
+    glob:
+      - ../../tests/t00057/t00057.c
+      - ../../tests/t00057/src/t00057_impl.c
+```
+## Source code
+File t00057.c
+```cpp
+#include "include/t00057.h"
+
+struct t00057_A {
+    int a1;
+};
+
+typedef struct t00057_B {
+    int b1;
+} t00057_B;
+
+struct t00057_C {
+    int c1;
+};
+
+union t00057_D {
+    int d1;
+    float d2;
+};
+
+struct t00057_E {
+    int e;
+    struct {
+        int x;
+        int y;
+    } coordinates;
+    union {
+        int z;
+        double t;
+    } height;
+};
+
+struct t00057_R {
+    struct t00057_A a;
+    t00057_B b;
+    struct t00057_C *c;
+    union t00057_D d;
+    struct t00057_E *e;
+    struct t00057_F *f;
+};
+
+```
+## Generated UML diagrams
+![t00057_class](./t00057_class.svg "Test case C99/C11 translation units with structs and unions")