[WIP] migration guide

[alexjeffburke]

This commit adds a first iteration of a migration guide for v11.

[sunesimonsen]

This is absolutely awesome, thanks you so much!

[papandreou]

This is great, thank you so much for picking this up!

I think I would put the #### sections in exactly the opposite order, so (what I perceive to be) the most impactful breaking changes would be mentioned first.

[alexjeffburke]

@sunesimonsen @papandreou this could do with a fresh read by both of you :)

[papandreou]

I think we need a way to control the order of the pages in the top menu, and maybe whether they appear there at all. It's pushing out the plugins page on small screens in portrait mode:

If we solve that, we should also move the Releases section to a separate page.

[sunesimonsen]

I don't want the migration to be a menu point, I don't think it is important enough for that. But let's solve that technically.

[alexjeffburke]

I think you're both right that this doesn't need to be a top level menu - only did that because it was easy. Perhaps Releases is the way to go and migration is linked to or something.

[alexjeffburke]

@papandreou have hopefully addressed all your comments in the last push :)

[papandreou]

Maybe the title should be "Migration to Unexpected 11"? Or maybe it would be better to also list migration guides for future versions here, but then the heading below (line 8) should be "Migration to Unexpected 11" or similar.

[papandreou]

Looks great! I guess what's missing is then:

• Add the capability to unexpected-documentation-site-builder to hide pages from the menu, via a flag in the front matter or similar
• Make the migration page hidden
• Add a "releases" page, probably also hidden from the menu, based on https://unexpected.js.org/#releases, also including a brief section for Unexpected 11 that links to the migration guide.
• Link to the "releases" page from the front page

Edit: The two last ones are fixed in #560