docs: describe the `foo@` revset syntax
We have supported multiple workspaces for six months now, but I forgot
to remove a note in the revset doc saying that we don't support
it. Also update the text to descibe how to refer to the working-copy
commit in another workspace.
@@ -22,9 +22,8 @@ ID or a Git ref pointing to them).
The symbol `root` refers to the virtual commit that is the oldest ancestor of
all other commits.
-The symbol `@` refers to the working copy commit in the current workspace (
-Jujutsu supports only one workspace per repo
-[so far](https://github.com/martinvonz/jj/issues/13)).
+The symbol `@` refers to the working copy commit in the current workspace. Use
+`<workspace name>@` to refer to the working copy commit in another workspace.
A full commit ID refers to a single commit. A unique prefix of the full commit
ID can also be used. It is an error to use a non-unique prefix.
