docs: update AVD profile description

[vonovak]

the previous description was ambiguous;

The required parameter is the id, not the name of the device. For old devices the values are the same, but for new ones they are not and so from the readme, you can't tell if name or id should be used, or if this matters at all (it does matter).

snippet from my avdmanager list device

---------
id: 22 or "Nexus 9"
    Name: Nexus 9
    OEM : Google
---------
id: 23 or "Nexus One"
    Name: Nexus One
    OEM : Google
---------
id: 24 or "Nexus S"
    Name: Nexus S
    OEM : Google
---------
id: 25 or "pixel"
    Name: Pixel
    OEM : Google
---------
id: 26 or "pixel_2"
    Name: Pixel 2
    OEM : Google
---------
id: 27 or "pixel_2_xl"
    Name: Pixel 2 XL
    OEM : Google

[ychescale9]

Thanks!