There's no particular user manual, no. Basic functionality hasn't changed; we'll document additional features with or shortly after the final release
.
Installation is indeed to just extract & run (though I'd recommend doing this somewhere local, e.g. ~/.local/bin, so that you can update from within the software without running it as sudo).
You also should run ./zotero not the bash script. Since 5.0 includes an Ubuntu desktop file, I think if you run it, you should see an icon in the unity launcher bar, which you can then "Lock to Launcher". There's a ticket for packaging Zotero for Ubuntu, but that's only going to happen if someone from the community picks it up.

Thank you @adamsmith and @dstillman ! Much appreciated. Really.

I ended up putting the extracted files in ~/.zotero/Zotero_linux-x86_64.

In fact there _IS_ a `run-zotero.sh` in 5.0 beta. I had a peek in it to understand what the script does and apparently it is used for debugging purposes. The question could well be in this case "did I download the right thing" ?

There is indeed a desktop entry file: `zotero.desktop` in the unpacked bunch of files and running it from its (above-mentioned) location creates a new one and puts it nicely where it belongs, i.e. in `~/.local/share/applications`.

However when I run the application either from the launchbar or from cli with fully qualified path, I get:
>> ERROR: Your Zotero database is currently in use.
>> Only one instance of Zotero using the same database may be opened
>> simultaneously at this time.
>> If Firefox with the Zotero extension is open, please close it and restart
>> Zotero Standalone.

Indeed I do have Firefox opened with the Zotero extension installed. What to do ? I need FF opened more or less "18/7/360" and Zotero at the same time with LO Writer when I write an article. Should I just get rid of the FF extension then ? But does not this preclude the use of Zotero to (in the best of cases) automatically import references from the web pages I visit ?

I may be confused as to how Zotero can be used but my (tentative) use case was:
- opened FF -> surf and fish for references as needed with Zotero extension
- opened Zotero Standalone -> insert citation in paper being written
- opened LO Writer -> process paper being written
... all that simultaneously.

Anything wrong with that ? Cheers. -ced.

@adamsmith:
All clear now. Thank you a bunch. I got rid of the installed FF extensions released with Zotero 4.x and installed the light-weight FF DB-connector you pointed me to instead. Sync'ed and connected all. All is working fine.

A word of explanation about spurious files in my Zotero directory. I first downloaded and installed the Zotero 4.0.x version.
I then downloaded the 5.0 beta version and unpacked it. Before unpacking I checked its destination and the default name of the destination directory. From v4.0.x to 5.0 the destination directory name did not change.
Seeing this I thought (wrongly) that `xarchiver` would crush the earlier destination directory. It did not; it appended to it !
Result: I have a nice mess of files pertaining to two different releases, among them the contentious one: `run-zotero.sh`. So, I owe you guys a "mea culpa".

So far having a bunch of irrelevant file does not seem to bother Zotero 5.0. However I will clean the mess up...

Cheers. -ced

Done. Tx.

One last musing:
I understand that saving refs to a distant DB administered by the Zotero project is done in the background. Is that the _only_ citation-DB available ?
Don't users have access to a local DB on their installation host too ? If so where ?

If no local-host DB is available by default, can a user secure a full snapshot-copy of their DB at any time ?

Cheers. -ced