docs(contributing): add Discord channels

[k9withabone]

Added the Podlet channels on the Podman Discord to the communication section of CONTRIBUTING.md.

Closes: #180

[TheRealBecks]

I would prefer the following changes:

• Make the Communication part more eye catchy like:

---

Communication

The Podlet project shares communication channels with other projects in the Containers organization.

On the Podman Discord, there are two dedicated channels for Podlet:

• #podlet for user discussions
• #podlet-dev for development of Podlet.

For discussions about issues, bugs, or features, feel free to create an [issue], [discussion], or [pull request] on GitHub.

---

• We should add (duplicate) the Communication section to the README.md and add it way more to the top, because users will most likely seek for some help and therefore checking the default Github page (= README.md), but they don't want to contribute and therefore won't find/check the CONTRIBUTION.md page. I would add it after the Feature section before the Install section