Minor edits to the XPath query help sheet

[greystate]

Prerequisites

• I have added steps to test this contribution in the description below

Description

This fixes a couple of inconsistencies, spelling-wise on the Multinode Treepicker's XPath query help sheet.

Also adds a note clarifying that the placeholder only works when used at the beginning of the query.

Testing the changes

Here's a couple of before and after screenshots to show the results of this PR - to test if it has been applied, create a new Datatype using the Multinode Treepicker and click the Query for root node with XPath link. Then click the Show XPath query help link and compare the screen with the "after" screenshot (or maybe just make sure that XPath is spelled consistently).

Before:

After:

[umbrabot]

Hi there @greystate, thank you for this contribution! 👍

While we wait for one of the Core Collaborators team to have a look at your work, we wanted to let you know about that we have a checklist for some of the things we will consider during review:

• It's clear what problem this is solving, there's a connected issue or a description of what the changes do and how to test them
• The automated tests all pass (see "Checks" tab on this PR)
• The level of security for this contribution is the same or improved
• The level of performance for this contribution is the same or improved
• Avoids creating breaking changes; note that behavioral changes might also be perceived as breaking
• If this is a new feature, Umbraco HQ provided guidance on the implementation beforehand
• The contribution looks original and the contributor is presumably allowed to share it

Don't worry if you got something wrong. We like to think of a pull request as the start of a conversation, we're happy to provide guidance on improving your contribution.

If you realize that you might want to make some changes then you can do that by adding new commits to the branch you created for this work and pushing new commits. They should then automatically show up as updates to this pull request.

Thanks, from your friendly Umbraco GitHub bot 🤖 🙂

[OwainWilliams]

Thanks @greystate - Good to get some consistancy and a bit of a tidy up. The note is also useful for those not used to XPath.

[nul800sebastiaan]

Cherry picked for v8.18 in 2fa31db