README.md broken link to project documentation

[tt4g]

README.md broken link to project documentation.

• json::array, json::object

  line 246: Note that in all these cases, you never need to "tell" the compiler which JSON value type you want to use. If you want to be explicit or express some edge cases, the functions [json::array](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_aa80485befaffcadaa39965494e0b4d2e.html#aa80485befaffcadaa39965494e0b4d2e) and [json::object](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_aa13f7c0615867542ce80337cbcf13ada.html#aa13f7c0615867542ce80337cbcf13ada) will help:

• json::parse()

  line 281: The above example can also be expressed explicitly using [json::parse()](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a5a0339361f3282cb8fd2f9ede6e17d72.html#a5a0339361f3282cb8fd2f9ede6e17d72):

• .get<std::string>()

  line 324: [.dump()](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a50ec80b02d0f3f51130d4abb5d1cfdc5.html#a50ec80b02d0f3f51130d4abb5d1cfdc5) always returns the serialized value, and [.getstd::string()](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a16f9445f7629f634221a42b967cdcd43.html#a16f9445f7629f634221a42b967cdcd43) returns the originally stored string value.