Fix encoding issues, grammar and formatting in onboarding documentation

Why is this change being made?

Continuation of !114214 (merged)

There are some typos in the onboarding documentation:

• related to laptops: specific models available [...] my vary [...]. Changed to may vary.
• related to malware: Windows is the platform most targetted [...]. Changed to targeted.

Additionally:

• Fixed special characters (e.g. ", ') interpreted as CP-1252 encoded instead of UTF-8

  Example of before:

• aligned laptop model descriptions (including correction of Gigabit (Gb) to Gigabyte (GB))

• removed gramatically incorrect commata for logically grouped enumerations

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 your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
  • 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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