Clarify step 3 about adding .cpp files

Author: ChrisThrasher

README.md

@@ -12,7 +12,7 @@ The template starts out very basic, but might receive additional features over t
 
 1. Follow the above instructions about how to use GitHub's project template feature to create your own project.
 1. Open [CMakeLists.txt](CMakeLists.txt). Rename the project and the executable to whatever name you want. The project and executable names don't have to match.
-1. Change the source files listed in [`add_executable`](CMakeLists.txt#L10) to match the source files your project requires.
+1. If you want to add or remove any .cpp files, change the source files listed in the [`add_executable`](CMakeLists.txt#L10) call in CMakeLists.txt to match the source files your project requires. If you plan on keeping the default main.cpp file then no changes are required.
 1. Configure and build your project. Most popular IDEs support CMake projects with very little effort on your part.
     - [VS Code](https://code.visualstudio.com) via the [CMake extension](https://code.visualstudio.com/docs/cpp/cmake-linux)
     - [Visual Studio](https://docs.microsoft.com/en-us/cpp/build/cmake-projects-in-visual-studio?view=msvc-170)