Document how to build this git repository to a kudo repository

[sharego]

As kubectl kudo package create command can zip a package, what can be using for a whole repository

[guenter]

Here are the commands to build a repository:

# Build one or more packages
./build-operator.sh repository/kafka/operator/

# Create the repository index
./build-community-repo.sh

This will give you a repository in build/repo.
We need to improve our docs around this and I edited the title to reflect that. See also #42