Clarify UX Heuristics

Why is this change being made?

There are two problems with the UX Heuristics page:

1. One sentence is missing the word "the".
2. Two heuristics sound the same and at first I thought they were redundant. @wleidheiser helped to clarify in this related Slack thread here, which I think would be beneficial context for others doing heuristic analyses in the future.

Visibility of system status	Real time user interface
Communicating the current state allows users to feel in control of the system, understand available actions and how to use them to reach their goal, and ultimately establishes trust the brand.	When a change of system status occurs, the interface instantly provides feedback to users.

Note that this change would also need to be reflected in the linked Heuristic Evaluation Scoresheet template.

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
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  • The when to get approval handbook section explains the workflow in more detail
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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