add guide

src/Camera.cpp

@@ -5,7 +5,7 @@
 #include <algorithm>
 #include <cmath>
 
-namespace planetarium {
+namespace engine {
 
 Camera::Camera() { reset(); }
 
@@ -68,4 +68,4 @@ glm::mat4 Camera::viewMatrix() const {
     return glm::lookAt(currentPosition_, currentFocus_, glm::vec3(0.0f, 1.0f, 0.0f));
 }
 
-}  // namespace planetarium
+}  // namespace engine