[Substrate.io Migration] Runtime Upgrades

[CrackTheCode016]

The "Runtime Upgrades" page was migrated from the existing Substrate.io Tutorial section: https://docs.substrate.io/maintain/runtime-upgrades/

[DrW3RK]

Before I go further into reviewing this PR, I would like to understand the scope of this document.

I see that this is under parachain-devs/parachain-maintenance which means the content can be streamlined to just that and the elaboration on forkless runtime upgrades, solo chains etc. which can live in the Polkadot protocol section which consists of the well written content from https://wiki.polkadot.network/docs/learn-runtime-upgrades

We can remove the info section on "Why Forkless" altogether and link to the forkless upgrades section elsewhere in the document when it is ready. wdyt?

[dawnkelly09]

@eshaben take a look at this and let me know what you think. We'll need CSS on admonitions/drop downs at some point

[eshaben]

Not sure what admonition style you're looking for, but the custom ones available are code, function, child, interface - if we don't have what you need, let me know!

[dawnkelly09]

@eshaben added an intro and took out the drop downs.

[eshaben]

Nice. LGTM!

If we need to change the scope of this or make modifications so this page better fits in it's final home (considering IA is being reviewed and updated right now), we can do that once we get to a more settled place

[0xLucca]

LGTM!