Documentation: ale-java eclipselsp customization

See also dense-analysis#2121

doc/ale-java.txt

@@ -114,9 +114,14 @@ Note: currently, the build can only run when launched with JDK 8. JDK 9 or more
 recent versions can be used to run the server though.
 
 After build completes the files required to run the language server will be
-located inside the folder |org.eclipse.jdt.ls.product/target/repository|.
+located inside the folder `org.eclipse.jdt.ls.product/target/repository`.
 Ensure to set |g:ale_java_eclipselsp_path| to the absolute path of that folder.
 
+You could customize compiler options and code assists of the server.
+Under your project folder, modify the file
+`.settings/org.eclipse.jdt.core.prefs` with options presented at
+https://help.eclipse.org/neon/topic/org.eclipse.jdt.doc.isv/reference/api/org/eclipse/jdt/core/JavaCore.html.
+
 g:ale_java_eclipselsp_path                         *g:ale_java_eclipselsp_path*
                                                    *b:ale_java_eclipselsp_path*