ADD: diff:ignoreChildren and diff:ignoreAttributes description to docs

[grishat]

Pull request description

Added diff:ignoreChildren and diff:ignoreAttributes missed description in docs.

I closed the PR #571, and opened this one.

Adjusted the text so it is more obvious that ignoreChildren only ignores children and not attributes. Same with the ignoreAttributes modifier.
Also added a note that attributes can be combined.

PR meta checklist

• Pull request is targeted at stable branch for documentation that is live on bunit.dev.
• Pull request is linked to all related issues, if any.
• I have read the CONTRIBUTING.md document.

Code PR specific checklist

• My code follows the code style of this project and AspNetCore coding guidelines.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• I have updated the appropriate sub section in the CHANGELOG.md.
• I have added, updated or removed tests to according to my changes.
  • All tests passed.

[grishat]

I'm sorry, but my english is bad (

[egil]

Thank you again for updating the PR.

A few tweaks to the language. Really good point about combining the two new diff modifiers.

[egil]

Lgtm. Thank you.