Users following the installation guide sometimes get stuck, reporting
that Elasticsearch has "hung" after running `./bin/elasticsearch`
because it doesn't exit, it just sits there in the foreground waiting
for something to happen. We do say that it "runs in the foreground" in
the docs but that's not clear enough, maybe folks expect it to declare
it started up successfully or to open a browser window for them or
something.
This commit expands the docs to clarify what users should expect from
running Elasticsearch from the command line and what they should do
next.
0534fbada8