Add for-users page

[csarven]

Resolves https://github.com/solid/solidproject.org/issues/859

for-users links to existing pages:

• https://solidproject.org/users/get-a-pod
• https://solidproject.org/apps

[csarven]

Noting here that the proposal names the page as "for-users" which follows the naming like "for-developers" and "for-organizations". However, I find the "for-" prefix unnecessary. At least in the case of "for-developers" and "for-organizations" it is unnecessary, and that they could just be "developers" and "organizations". There is additional complication around using "users" instead of "for-users" because if and when the Solid Project uses a Solid server, there is some potential issue ahead since there are URIs like https://solidproject.org/users/get-a-pod , and that reserves the name "users" for a container.

Emphasising again why solidproject.org's Sitemap is an essential piece for proper overview and maintenance of the website.