Update contribution guideline to non-zero major versions (#225 / #333)
Update contribution guideline to non-zero major versions (#225 / #333)

The contribution guidelines mentioned that the major version "stays
at 0 for now". Change that to account for the looming 1.0 release,
after which new major version increases will be decided by the
maintainer.

Closes: #225
PR: #333
CodeFX-org/junit-io