chore: Add Watcher Setup guide

[lindnerby]

Description

Changes proposed in this pull request:

• Add a step-by-step guide for Kyma teams to setup the Watcher mechanism for their component
• Re-structure and update listener pkg description

Related issue(s)

• PoC: SKR Watch on Module Resources #488

[mmitoraj]

I've added a few suggestions. In addition could you:

• change the file name from "Listener.md" to lowercase: "listener.md"?
• change the file name "guide.md" to something more meaningful, for example, "configure-watcher.md" or "watcher-set-up-guide.md", etc.? Remember to update paths later on.
• See the local file with the suggestions for the guide itself :)

[lindnerby]

I've added a few suggestions. In addition could you:

• change the file name from "Listener.md" to lowercase: "listener.md"?
• change the file name "guide.md" to something more meaningful, for example, "configure-watcher.md" or "watcher-set-up-guide.md", etc.? Remember to update paths later on.
• See the local file with the suggestions for the guide itself :)

Sure, applied your suggestions @mmitoraj
Please take a look