docs: update BUILD.md to use ccache and ninja

Signed-off-by: black-desk <me@black-desk.cn>

BUILD.md

@@ -10,6 +10,14 @@ sudo cmake --install build-release
 For developing or debugging linglong:
 
 ```bash
+
+# Use ccache and ninja if available.
+# You might want add this to the rc file of your shell.
+export CMAKE_CXX_COMPILER_LAUNCHER=="$(command -v ccache 2>/dev/null)"
+if command -v ninja &>/dev/null; then
+        export CMAKE_GENERATOR="Ninja"
+fi
+
 # configure, build and test
 cmake --workflow --preset debug
 

BUILD.zh_CN.md

@@ -10,6 +10,8 @@ sudo cmake --install build-release
 如果你想开发或调试玲珑：
 
 ```bash
+export CMAKE_CXX_COMPILIER_LAUNCHER="$(command -v ccache)"
+
 # 配置，构建然后运行测试
 cmake --workflow --preset debug