Requiring Boost when STL have improper std::filesystem support

CHN-02-安装.md

@@ -16,7 +16,7 @@
 *  OpenSSL，并非必须，如果安装了OpenSSL库，drogon将支持HTTPS，否则drogon只支持HTTP；
 *  c-ares, 并非必须，如果安装了ares库，drogon对DNS的支持会具有更好的性能；
 *  libbrotli，并非必须，如果安装了brotli库，drogon的HTTP响应会支持brotli压缩；
-*  boost，版本**不低于1.61**，只在C++编译器不支持c++17时才需要安装；
+*  boost，版本**不低于1.61**，只在C++编译器不支持c++17或STL库不完整支持`std::filesystem`时才需要安装；
 *  postgreSQL, mariadb, sqlite3的客户端开发库，并非必须，安装后drogon会提供对响应的库的访问能力；
 *  gtest, 并非必须，如果安装了gtest库，drogon的单元测试代码可以被编译；
 
@@ -208,4 +208,4 @@ vcpkg.exe install drogon:x64-windows
 
 我们也在[docker hub](https://hub.docker.com/r/drogonframework/drogon)上提供了构建好的docker镜像. 在这个docker里Drogon和它所有的依赖都已经安装完毕，用户可以在上面直接开发Drogon应用程序。
 
-# 03 [快速开始](CHN-03-快速开始)
+# 03 [快速开始](CHN-03-快速开始)

ENG-02-Installation.md

@@ -16,7 +16,7 @@ This section takes Linux as an example to introduce the installation process. Ot
 * OpenSSL, not mandatory, if the OpenSSL library is installed, drogon will support HTTPS as well, otherwise drogon only supports HTTP.
 * c-ares, not mandatory, if the c-ares library is installed，drogon will be more efficient with DNS;
 * libbrotli, not mandatory, if the libbrotli library is installed, drogon will support brotli compression when sending HTTP responses;
-* boost, the version should be **no less than 1.61**, is required only if the C++ compiler does not support C++ 17.
+* boost, the version should be **no less than 1.61**, is required only if the C++ compiler does not support C++ 17 and if the STL doesn't fully support `std::filesystem`.
 * the client development libraries of postgreSQL, mariadb and sqlite3, not mandatory, if one or more of them is installed, drogon will support access to the according database.
 * gtest, not mandatory, if the gtest library is installed, the unit tests can be compiled.