Change the prompt of alternative media description field to be more inclusive

[jakobrosin]

Currently, the field prompt says “Describe for visually impaired people.”
Since media descriptions can be applied for videos and audio as well, the description for a particular media can be useful for different users.
Potential prompts to discuss:

• Describe the contents of uploaded media
• Describe the visuals, sounds or spoken word of the media
• Describe content for people with disabilities

[NickColley]

I think it's important that people understand who it is benefiting the most but agree it could be better so lets improve this for sure.