Make printing tips optional

[nkakouros-nordsnipe]

It's good to see this text the first times you use stack-pr:

This stack is ready to land!

If you'd like to push your local changes first, you can use the following command to update the stack:
  $ stack-pr export -B unittest-ruff~5 -H unittest-ruff

To land it, you could run:
  $ stack-pr land -B unittest-ruff~5 -H unittest-ruff

If you'd like to land stack except the top N commits, you could use the following command:
  $ stack-pr land -B unittest-ruff~5 -H unittest-ruff~N

If you prefer to merge via the github web UI, please don't forget to edit commit message on the merge page!
If you use the default commit message filled by the web UI, links to other PRs from the stack will be included in the commit message.

But after a while it does not add any value and it becomes too verbose.

[ZolotukhinM]

Fixed by #108 (will be included in the next release)