Update stale community channel references (freenode, puppet-users mailing list)

[miharp]

Several pages still reference defunct community channels (freenode IRC, puppet-users/puppet-dev Google Groups). These should be updated to point to voxpupuli.org/connect.

Affected files

• docs/_openvox_8x/experiments_overview.markdown — lines 18, 45, 46: references puppet-users/puppet-dev mailing lists and freenode IRC
• docs/_openvoxdb_8x/CONTRIBUTING.md — line 296: references #puppet-dev on freenode.org