Remove mention to 'putup' in the CONTRIBUTING template
Remove mention to 'putup' in the CONTRIBUTING template

… additionally also replace the reference to `master` with `main`.
(Currently GitHub instruct users to rename their master branch to main
in the first push. Moreover `main` is more generic if we consider it as
an adjective instead of a noun and therefore can also refer to
`master` since it is the main branch after all...)

blue-yonder/pyscaffold,blue-yonder/pyscaffold