Documentation: Remaining tasks

[adpaco-aws]

Will keep adding stuff that cannot be done now (during #700 ) but has to be done.

• Update project status (in introduction)
• Update project status (in README.md) (project status doesn't appear in README.md)
• Review installation guide
• Make edits to "Usage - On a package" once Run all proof harnesses by default #962 is complete.
• Review wording in "Limitations"
• Consider if other topics should appear in "Rust feature support"

[adpaco-aws]

After #1160 all tasks have been completed.