Add `ddev-get` topic to help others find addon

[tyler36]

Please consider adding a ddev-get topic to the repo.

This will allow others to find this addon by using: ddev get --list --all

Steps

1. Click the "cogs" icon

2. Add ddev-get as a topic.

3. Run ddev get --list --all and check if this repo appears (should appear within a minute).

[justafish]

done, thank you!

[tyler36]

Confirmed. Just checked and it's discoverable.

Thank you.