JetBrains: Add custom keymap docs

Created by: philipp-spiess

Adds a short explainer on how to overwrite keymaps. Thanks @unknwon for the screenshot

Test plan

docs change

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.

Created by: taras-yemets

Review: Approved

Created by: jjinnii

Review: Approved

LGTM! Thanks for updating our docs

Merged by: philipp-spiess at 2022-08-11 12:44:03 UTC

Created by: vdavid

Review: Commented

Nice, thanks, @philipp-spiess!