The command used to invoke the language server is missing some options
to include additional java modules. Without these modules the server
was not working properly.
The correct command can be found in a `launcher` script on the same
directory the `java` executable for the language server is found.
This commit changes the docs to prefer the launcher script over the java
executable. For backward compatibility it also fixes the command
invocation in case the java executable is configured.
The command used to invoke the LSP process was being escaped wrong.
Also added a new option to set a different java executable and fixed the
documentation.
