As a convention, modules should be placed in another directory and then
get selectively enabled by symlinking.
Currently, all modules are placed in ./modules-available, and the symlinks
reside in ./modules
Note that you can name the symlink differently. The name of the symlink
will define by what identifier the module is referred to. This way
you can have different implementations or versions of the same module
and switch them out.
An example of this is the module "serversetup-bwlp" which is symlinked
as just "serversetup", so we can have "serversetup-cdn" in the future,
as it seems the two locations have quite different requirements for this
module's functionality.

Note that a module identifier cannot contain dashes (-), so this is an
easy way to hint that a module is supposed to be aliased when being
activated.