Adding note regarding uninstalling binaries before source build (open…

…-rmf#160)

Signed-off-by: Aaron Chong <[email protected]>

README.md

@@ -86,7 +86,9 @@ rosdep install --from-paths src --ignore-src --rosdistro galactic -y
 
 ### Compiling Instructions
 
-On `Ubuntu 20.04`:
+> NOTE: Due to newer changes in the source build, there might be conflicts and compilation errors with older header files installed by the binaries. Please remove the binary installations before building from source, using `sudo apt remove ros-galactic-rmf*`.
+
+Compiling on `Ubuntu 20.04`:
 
 ```bash
 cd ~/rmf_ws