Newcomers_Guide.rst: Verify issue exists
Newcomers_Guide.rst: Verify issue exists

This adds a step in the Newcomers guide
to verify the issue exists.

Closes https://github.com/coala/coala/issues/5802

Co-authored-by: pilgrim2308 <14d59feb373bc2e19a0c2862de369080a551d3e6@gmail.com>

coala/coala,coala/coala,coala/coala