Components: Include stylesheet in usage instructions.

[iandunn]

Without these it's easy to think something is broken, or that you're doing something wrong, until you realize that it's just that the missing CSS. Documenting this will save time and frustrating.

[gziolo]

It seems like a great idea to add this note. I'm wondering whether we should add a similar note to all packages which also ship styles like block-library or format-library.

[gziolo]

There is an unrelated issue with e2e test:

https://travis-ci.com/WordPress/gutenberg/jobs/196208309#L1161

FAIL specs/block-hierarchy-navigation.test.js (7.863s)
  ● Navigating the block hierarchy › should navigate block hierarchy using only the keyboard
    expect(received).toMatchSnapshot()
    Snapshot name: `Navigating the block hierarchy should navigate block hierarchy using only the keyboard 1`
    - Snapshot
    + Received
    @@ -9,9 +9,13 @@
      <div class="wp-block-column"></div>
      <!-- /wp:column -->
      
      <!-- wp:column -->
      <div class="wp-block-column"><!-- wp:paragraph -->
    - <p>Third column</p>
    + <p></p>
      <!-- /wp:paragraph --></div>
      <!-- /wp:column --></div>
    - <!-- /wp:columns -->"
    + <!-- /wp:columns -->
    + 
    + <!-- wp:image -->
    + <figure class="wp-block-image"><img alt=""/></figure>
    + <!-- /wp:image -->"
      80 | 		await page.keyboard.type( 'Third column' );
      81 | 
    > 82 | 		expect( await getEditedPostContent() ).toMatchSnapshot();
         | 		                                       ^
      83 | 	} );
      84 | 
      85 | 	it( 'should appear and function even without nested blocks', async () => {
      at Object.toMatchSnapshot (specs/block-hierarchy-navigation.test.js:82:42)
      at tryCatch (../../node_modules/regenerator-runtime/runtime.js:62:40)
      at Generator.invoke [as _invoke] (../../node_modules/regenerator-runtime/runtime.js:288:22)
      at Generator.prototype.(anonymous function) [as next] (../../node_modules/regenerator-runtime/runtime.js:114:21)
      at asyncGeneratorStep (specs/block-hierarchy-navigation.test.js:9:103)
      at _next (specs/block-hierarchy-navigation.test.js:11:194)

It's an interminient failure and I'm documenting it only so I could reference it in a follow-up PR where I will disable it.

[iandunn]

I think that's a good idea, I opened #15253 to track that.