Added a reference to dvc cache dir in shared-development-server page

[PseudoNerd]

fix #986
Modified shared-development-server page to show the usage of dvc cache dir command and added a description to the dvc cache dir page for better understanding.

[jorgeorpinel]

Please link to the issue this PR addresses or closes (see https://help.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue). This is mentioned in the pull request template. There's no need to delete that text BTW 🙂

[jorgeorpinel]

Thanks for the updates @PseudoNerd I'll check them out ASAP. Please notice the CI test is failing at the md format check (see https://circleci.com/gh/iterative/dvc.org/3556). Did you setup the local dev environment completely as explained in the contrib guide? #1321 was opened automatically to fix the formatting (so you could merge that for now), but ideally you can keep the formatting same from your IDE, enjoying the Git hooks that check this for you before git push.

[jorgeorpinel]

The main changes to content/docs/use-cases/shared-development-server.md are correct but the other changes have some issues.

[jorgeorpinel]

Thank you @PseudoNerd! Let's chat about your project ideas soon, and if you can please continue to contribute to other small issues when you have time.