Add a information about app-designer

[wbrunette]

If you download the zip of app designer it is supposed to contain a version with all the npm packages so grunt will work.

However, if you check it out using git you need to run the following command:
"npm install" to get the npm packages.

Update this page to properly reflect this information:
https://docs.odk-x.org/app-designer-install/

[sonalgaud12]

@wbrunette Hello Sir!
Pr raised please check.
Thank you!

[xadina02]

Hello @wbrunette
Is this issue still open for tackle?
Can I be assigned to work on this?

[Redeem-Grimm-Satoshi]

Hello @wbrunette Is this issue still open for tackle? Can I be assigned to work on this?

@sonalgaud12 is currently working on the issue. For now feel free to check other issues

[Chandrakeer]

Hello, this is my first time contributing to an open-source project through Outreachy. Could I please be assigned this task?