The mvn-repo subdirectory must be structured as a Maven repository, so it shouldn't be edited by hand.
To add the file example-1.0.jar as com.example:example version 1.0, use the following command line.

$ mvn install:install-file -Dmaven.repo.local=mvn-repo -Dfile=example-1.0.jar -DgroupId=com.example -DartifactId=example -Dversion=1.0 -Dpackaging=jar -DgeneratePom=true