Added a separate README for building the tests

Author: liuzicheng1987

tests/README.md

@@ -0,0 +1,52 @@
+# Compiling and running the tests
+
+reflect-cpp uses vcpkg for dependency management, including
+gtest, which is required for the tests.
+
+```bash
+# bootstrap vcpkg if you haven't done so already 
+git submodule update --init
+./vcpkg/bootstrap-vcpkg.sh # Linux, macOS
+./vcpkg/bootstrap-vcpkg.bat # Windows
+# You may be prompted to install additional dependencies.
+```
+
+## JSON only
+
+To compile the tests, do the following:
+
+```bash
+cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DREFLECTCPP_BUILD_TESTS=ON
+cmake --build build -j 4 # gcc, clang
+cmake --build build --config Release -j 4 # MSVC
+```
+
+To run the tests, do the following:
+
+```
+./build/tests/json/reflect-cpp-json-tests
+```
+
+## All serialization formats
+
+To compile the tests with serialization formats other than JSON, do the following:
+
+```bash
+cmake -S . -B build -DREFLECTCPP_BUILD_TESTS=ON -DREFLECTCPP_BSON=ON -DREFLECTCPP_CBOR=ON -DREFLECTCPP_FLEXBUFFERS=ON -DREFLECTCPP_MSGPACK=ON -DREFLECTCPP_XML=ON -DREFLECTCPP_TOML=ON -DREFLECTCPP_UBJSON=ON -DREFLECTCPP_YAML=ON -DCMAKE_BUILD_TYPE=Release
+cmake --build build -j 4 # gcc, clang
+cmake --build build --config Release -j 4 # MSVC
+```
+
+To run the tests, do the following:
+
+```
+./build/tests/bson/reflect-cpp-bson-tests
+./build/tests/cbor/reflect-cpp-cbor-tests
+./build/tests/flexbuffers/reflect-cpp-flexbuffers-tests
+./build/tests/msgpack/reflect-cpp-msgpack-tests
+./build/tests/json/reflect-cpp-json-tests
+./build/tests/toml/reflect-cpp-toml-tests
+./build/tests/toml/reflect-cpp-ubjson-tests
+./build/tests/xml/reflect-cpp-xml-tests
+./build/tests/yaml/reflect-cpp-yaml-tests
+```