docs: describe known limitations

[HonkingGoose]

Changes:

• Describe Renovate's known limitations

Context:

We should set proper expectations with regards to Renovate bot's performance.
People like to imagine a super fast and powerful bot, that will do anything they can throw at it.
So we should explain what the bot can and cannot do for the user, and explain why we have some limitations.

Some things are a design decision, and other things are on our todo list.
For things that are on our todo list, we should mention issues that the reader can follow.

Inspired by discussion: #11884

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[HonkingGoose]

I know this is a really, really rough draft! I'm trying to feel out what we need to cover, and I don't know the ins and outs of the bot.... 😉

[rarkins]

I'm ok to start with this and improve it over time

[HonkingGoose]

Okay! I don't have anything meaningful to add anyways... 😄 😉

[renovate-release]

🎉 This PR is included in version 27.25.0 🎉

The release is available on:

• GitHub release
• 27.25.0

Your semantic-release bot 📦🚀