Add explicit source path in cmake invocation

Otherwise CMake aborts with an error.

src/includes/getting-started-install/native.mdx

@@ -6,7 +6,7 @@ For example, `CMake` can be used like this (on macOS):
 
 ```shell
 # configure the cmake build into the `build` directory, with crashpad (on macOS)
-cmake -B build -D SENTRY_BACKEND=crashpad --config RelWithDebInfo 
+cmake -B build -D SENTRY_BACKEND=crashpad --config RelWithDebInfo -S .
 # build the project
 cmake --build build --config RelWithDebInfo --parallel
 # install the resulting artifacts into a specific prefix