Fix compile error with _HAS_STATIC_RTTI=0 (#4046)

docs/mkdocs/docs/api/macros/json_has_static_rtti.md

@@ -0,0 +1,31 @@
+# JSON_HAS_STATIC_RTTI
+
+```cpp
+#define JSON_HAS_STATIC_RTTI /* value */
+```
+
+This macro indicates whether the standard library has any support for RTTI (run time type information).
+Possible values are `1` when supported or `0` when unsupported.
+
+## Default definition
+
+The default value is detected based on the preprocessor macro `#!cpp _HAS_STATIC_RTTI`.
+
+When the macro is not defined, the library will define it to its default value.
+
+## Examples
+
+??? example
+
+    The code below forces the library to enable support for libraries with RTTI dependence:
+
+    ```cpp
+    #define JSON_HAS_STATIC_RTTI 1
+    #include <nlohmann/json.hpp>
+
+    ...
+    ```
+    
+## Version history
+
+- Added in version ?.