Required setup chunk opts

[krystian8207]

Thank you @RLesur for the great package, it made my life much easier!

About the issue.
I used to have the following chunk setup in my current project:

```{r setup, include = FALSE}
knitr::opts_chunk$set(echo = TRUE, eval = TRUE, comment = NA,
                      message = FALSE, warning = FALSE, results = FALSE)
```

Nevertheless, global results=FALSE seems to stop working klippy properly.

It seems that results=TRUE is necessary what actually helped me to solve the issue.

```{r klippy, echo=FALSE, include=TRUE, results=TRUE}
klippy::klippy()
```

Could you include this in the documentation? I think it can spare some time for future users.
Thank!

Best,
krystian8207