📝 add more API documentation

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

@@ -0,0 +1,78 @@
+# basic_json::update
+
+```cpp
+// (1)
+void update(const_reference j);
+
+// (2)
+void update(const_iterator first, const_iterator last);
+```
+
+1. Inserts all values from JSON object `j` and overwrites existing keys.
+2. Inserts all values from from range `[first, last)` and overwrites existing keys.
+
+The function is motivated by Python's [dict.update](https://docs.python.org/3.6/library/stdtypes.html#dict.update) function.
+
+## Parameters
+
+`j` (in)
+:   JSON object to read values from
+
+`first` (in)
+:   begin of the range of elements to insert
+
+`last` (in)
+:   end of the range of elements to insert
+
+## Exceptions
+
+1. The function can throw thw following exceptions:
+    - Throws [`type_error.312`](../../home/exceptions.md#jsonexceptiontype_error312) if called on JSON values other than objects;
+      example: `"cannot use update() with string"`
+2. The function can throw thw following exceptions:
+    - Throws [`type_error.312`](../../home/exceptions.md#jsonexceptiontype_error312) if called on JSON values other than objects;
+      example: `"cannot use update() with string"`
+    - Throws [`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) if called on an iterator which does not belong
+      to the current JSON value; example: `"iterator does not fit current
+      value"`
+    - Throws [`invalid_iterator.210`](../../home/exceptions.md#jsonexceptioninvalid_iterator210) if `first` and `last` do not belong to the
+      same JSON value; example: `"iterators do not fit"`
+
+## Complexity
+
+1. O(N*log(size() + N)), where N is the number of elements to insert.
+2. O(N*log(size() + N)), where N is the number of elements to insert.
+
+## Example
+
+??? example
+
+    The example shows how `update()` is used.
+    
+    ```cpp
+    --8<-- "examples/update.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/update.output"
+    ```
+
+??? example
+
+    The example shows how `update()` is used.
+    
+    ```cpp
+    --8<-- "examples/update__range.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/update__range.output"
+    ```
+
+## Version history
+
+- Added in version 3.0.0.