Updates AboutStrings with new examples

[indented-automation]

PR Summary

Fixes #297

Context

Adds a few new examples to AboutStrings covering expansion of non-existent variables and expansion of variables within a non-existent scope / provider.

Replaces simpler with "more easily" (grammar :)).

Changes

• Adds 'will expand variables that do not exist'
• Adds 'can get confused about :'
• Adds 'can use curly braces to define the variable name in a string with :'
• 'can be done simpler' to 'can be done more easily'

Checklist

• Pull Request has a meaningful title.
• Summarised changes.
• Pull Request is ready to merge & is not WIP.
• Added tests / only testable interactively.
  • Make sure you add a new test if old tests do not effectively test the code changed.
• Added documentation / opened issue to track adding documentation at a later date.

[vexx32]

Looks good, thank you! 😊 💖