[doc] Installation is recommended but not mandatory (only external dependencies must be installed).

[dlyr]

"Installed demo/apps will be redistribuable, not installed demo or app should be executed only from buildtree).

I think we should be more precise saying that installation is recommended but not mandatory (only external dependencies must be installed). Installed demo/apps will be redistribuable, not installed demo or app should be executed only from buildtree.

In this case, in the usage section (file radium-as-submodule.md - should we rename it as radium-client.md), we should indicate how to use Radium from its build tree, the only thing that will change will be to set, at configure time of the client app/lib/plugin :
CMAKE_PREFIX_PATH=/path/to/radium/buildtree/src or to define Radium_DIR=/path/to/radium/buildtree/src. "

Originally posted by @MathiasPaulin in #1057 (comment)