Update Content Community of Practice text

We've received a request to update the content regarding our content community of practice on dta.gov.au. The request included some references to Guides.

## What do you need?

On https://guides.service.gov.au/content-guide/, can you please update the text reading `Join our government content community to make suggestions and provide feedback.` to read, `Join our government [Content Community of Practice](https://www.dta.gov.au/help-and-advice/communities-practice#content-design-and-strategy-community) to make suggestions and give feedback. To join, email [content@dta.gov.au](mailto:content@dta.gov.au)`?