fix #956 improve get_golem_options doc

[VincentGuyader]

new doc is :

# Define and use golem_options
if (interactive()) {
  # 1. Pass parameters directly to `run_app`

  run_app( title="My Golem App", 
           content = "something" )

  # 2. Get the values 
  # 2.1 from the UI side

  h1(get_golem_options("title"))

  # 2.2 from the server-side

  output$param <- renderPrint({
    paste("param content = ", get_golem_options("content"))
  })
  
  output$param_full <- renderPrint({
     get_golem_options() # list of all golem options as a list.
  })
  
  # 3. If needed, to set default value, edit `run_app` like this :

  run_app <- function(
             title = "this",
             content = "that",
             ...
  ) {
    with_golem_options(
      app = shinyApp(
        ui = app_ui,
        server = app_server
      ),
      golem_opts = list(
      title = title,
      content = content,
      ...
      )
    )
  }
   
  
}