Most of our samples simply include .composite files on the classpath, i.e. under the target/classes dir as generated by mvn. The Tuscany contribution service will look here and load any .composite files that it finds. There are other alternatives
sca-contributions
META-INF/sca-deployables
If you have a contribution in a directory say.
/my/contribution/dir
Then all components in composites under /META-INF/sca-deployables will be automatically be included in the deployable list maintained by the contribution, for example
/my/contribution/dir/META-INF/sca-deployables/mycomposite.composite