How can I add a dependency after I have created a package?

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Hi all,

I created a package called demo. It has two dependencies

1) roscpp

2) robot_comm

Now I want to interface it with a sensor, so I created a node called 'cell_node' for the sensor. I plan to use information from a topic in 'cell_node' which publishes the message 'loadMsg' at 50Hz.

But then, I am getting an error

cell_node/loadMsg.h : No such file or directory.

I kind of know why this is happening. It is because I never added cell_node to the list of dependencies when I first created my package demo.

My question is, how can I add a new dependency to an already existing package, so that it compiles code in that dependency too?

Thanks! All help is appreciated :)