Add a section for portable version in the installation guide

[Xpirix]

Proposed fix for #414

Hi @timlinux and @anitagraser , what do you think about adding this section?

[anitagraser]

I'm not aware that any portable is officially endorsed. Please wait for official confirmation.

[pigreco]

As I wrote in issue #414, it would be useful to have a section, on the QGIS site, to download portables and not the code to create them.
The end user only needs the download.

[Xpirix]

I'm not aware that any portable is officially endorsed. Please wait for official confirmation.

Sure @anitagraser , I've converted it to draft for now. Thank you for the feedback.

As I wrote in issue #414, it would be useful to have a section, on the QGIS site, to download portables and not the code to create them.
The end user only needs the download.

@pigreco Ah, I understand. So, your suggestion is that the QGIS releases include portable versions (as demonstrated in the code example) and provide download links on the website. In this case, it might be more appropriate to report the issue to the QGIS core repository first.
However, if the download links are already available, I’m willing to assist in integrating them into the website.

Regards.