[macOS] ns help generates EACCES Permission Denied

[fossette]

Environment

• macOS Catalina 10.15.5, using an account having the administrator privileges
• CLI: 7.0.11 (iOS and Android setup)
• Your current package manager is npm 6.14.8
• XCode Version: 12.2 (12B45b)

Describe the bug, runtime error
(I think) I followed the macOS install procedure. I somehow ended-up with a missing
/usr/local/lib/node_modules/nativescript/docs/html system directory.

To Reproduce
Run ns help when the /usr/local/lib/node_modules/nativescript/docs/html system directory is missing.
EACCES: permission denied, mkdir '/usr/local/lib/node_modules/nativescript/docs/html'

Expected behavior
Check for relevant credentials before executing the mkdir command, and propose to run using sudo to work arround this issue.

Sample project
Not required

Additional context
Similar to: #3694