📝 mentioned value function on main doc page #570

doc/index.md

@@ -27,6 +27,7 @@ These pages contain the API documentation of JSON for Modern C++, a C++11 header
     - @link nlohmann::basic_json::get_ptr get_ptr @endlink -- get a value pointer
     - @link nlohmann::basic_json::get_ref get_ref @endlink -- get a value reference
     - @link nlohmann::basic_json::operator ValueType() const operator ValueType @endlink -- get a value (implicit conversion)
+    - @link nlohmann::basic_json::value value @endlink -- get a value from an object and return default value if key is not present
   - lexicographical comparison operators
   - serialization
   - deserialization