Minor edits to demo - installation instructions / option of adding image via url

[Godofnothing]

Changes

Installation instructions:

• Added option of cloning and installing via python setup.py. This option is preferrable if one is using assets for demo.
• Added diffusers to requirements.

Demo:

• Added option of loading image via url.

Descprition:

• Baseline SD decoder is VAE rather than GAN.

Error for Windows users:

• According to the issue con.png is not allowed name in Windows environment.