📝 add more API documentation

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

@@ -0,0 +1,59 @@
+# basic_json::find
+
+```cpp
+template<typename KeyT>
+iterator find(KeyT&& key);
+
+template<typename KeyT>
+const_iterator find(KeyT&& key) const
+```
+
+Finds an element in a JSON object with key equivalent to `key`. If the element is not found or the JSON value is not an
+object, `end()` is returned.
+
+## Template parameters
+
+`KeyT`
+:   A type for an object key.
+
+## Parameters
+
+`key` (in)
+:   key value of the element to search for.
+    
+## Return value
+
+Iterator to an element with key equivalent to `key`. If no such element is found or the JSON value is not an object,
+past-the-end (see `end()`) iterator is returned.
+
+## Exception safety
+
+Strong exception safety: if an exception occurs, the original value stays intact.
+
+## Complexity
+
+Logarithmic in the size of the JSON object.
+
+## Notes
+
+This method always returns `end()` when executed on a JSON type that is not an object.
+
+## Example
+
+??? example
+
+    The example shows how `find()` is used.
+    
+    ```cpp
+    --8<-- "examples/find__key_type.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/find__key_type.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.