Revise the Community Roles exercise

### How could the content be improved?

I am currently teaching with @sstevens2 and we'd like to recommend that we change the Community Roles exercise to be as follows:

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Spend some time to browse through some of the community roles and their descriptions on [The Carpentries community website](https://carpentries.org/community/) at https://carpentries.org/community/.

Write:

A question that you have (or that you imagine someone else might have) about the role.
Are there any roles that already draw your interest, and you might like to be involved with?
Are there roles you would like to see that are not listed? Note that, too!

Curriculum Advisors - guide the development of existing lessons.
Code of Conduct Committee - keeps our community friendly and welcoming.
Board of Directors - make up the governance and policy portion of The Carpentries.
Instructors - teach and sometimes organise workshops.
Lesson Maintainers - support existing lessons.
Instructor Trainers - train and support our new Instructors.
Lesson Program Governors - oversee and guide the strategy and health of The Carpentries Lesson Programs
Lesson Developers - help our community adapt to evolving training needs by creating new lessons

This exercise should take about 5 minutes.

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We appreciate that asking them to write a brief definition of the role, as the current exercise does, gives us a sense of how well they understand the different roles, but the updated website does define roles in some detail, and they can always return to it for clarity at some later stage.

### Which part of the content does your suggestion apply to?

https://carpentries.github.io/instructor-training/15-carpentries.html#a-culture-of-contribution

Start at the linked “A Culture of Contribution” section and compare the current Community Roles exercise with the proposed wording. Check the Carpentries community page for the listed role descriptions, then update the lesson content so the exercise matches the requested questions and remains about five minutes long.

Written by the indexing model from the issue text.