docs(vignette): remove warning message when airGR is loaded in get_started

vignettes/V01_get_started.Rmd

@@ -48,7 +48,7 @@ In the following example, we use a data sample contained in the package. For rea
 
 First, it is necessary to load the **airGR** package:
 
-```{r}
+```{r, warning=FALSE}
 library(airGR)
 ```