Accessibility-insights-web: Add more detail to automated checks role

[ferBonnin]

Describe the bug
From user feedback, emphasize the role of automated checks in the tool: "that no automated tool can find even a majority of accessibility defects on a web page"

To Reproduce
Steps to reproduce the behavior:

1. Go to https://www.washington.edu/accesscomputing/AU/before.html
2. Run automated checks

OR

1. Go to https://accessibilityinsights.io/docs/en/web/getstarted/fastpass

Expected behavior
The Automated checks section of FastPass should clarify that it only finds some of the most common accessibility issues

Are you willing to submit a PR?

Yes

Did you search for similar existing issues?

Yes

[ferBonnin]

@LiLoDavis can you help us draft the language for this?

[LiLoDavis]

@ferBonnin How about this? The "Did you know?" part is a bit of a trick to get people to look at the text.

Did you know?
Automated checks can identify some common accessibility problems, such as missing or invalid properties. Most accessibility problems can be detected only through manual testing.

[ferBonnin]

@LiLoDavis I like this! Do we want to mention that they can use Assessment too?

[LiLoDavis]

@ferBonnin Good idea. How about this?

Did you know?
Automated checks can detect some common accessibility problems, such as missing or invalid properties. However, most accessibility problems can be identified only through manual testing. The most reliable way to evaluate the accessibility of a website or web app is to complete an assessment.

[ferBonnin]

@LiLoDavis looks great. I would just modify to add 'compliance':
Did you know?
Automated checks can detect some common accessibility problems, such as missing or invalid properties. However, most accessibility problems can be identified only through manual testing. The most reliable way to evaluate the accessibility compliance of a website or web app is to complete an assessment.

[LiLoDavis]

@ferBonnin I approve!

[dbjorge]

@ferBonnin @LiLoDavis can you clarify exactly where in the UI/docs you want this new text to show up? (an annotated screenshot would be the most helpful for me :) )

[ferBonnin]

@dbjorge only in the UI (already added it in the docs). Will send you a screenshot

[dbjorge]

To clarify: it should render in the fastpass view only, in between the <h1>{this.props.title}</h1> and the this.renderContent() in the IssuesTable within the details view main content. Probably we'd do this by adding an optional subTitle to IssuesAdHocVisualization.displayableData and rendering it in IssuesTable iff present.

It should be styled as $secondary-text.

[dbjorge]

Fix is implemented in #632, but need to wait til Chelsea is back in the office to review and continue