📝 add more API documentation

doc/mkdocs/docs/api/basic_json/~basic_json.md

@@ -0,0 +1,19 @@
+# basic_json::~basic_json
+
+```cpp
+~basic_json() noexcept
+```
+
+Destroys the JSON value and frees all allocated memory.
+
+## Exception safety
+
+No-throw guarantee: this member function never throws exceptions.
+
+## Complexity
+
+Linear.
+
+## Version history
+
+- Added in version 1.0.0.