adding example specifying conf level in ard_survival_survfit() (#217)

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(#<issue number>, @<username>)

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**Reference GitHub issue associated with pull request.** _e.g., 'closes
#<issue number>'_
closes #216


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R/ard_survival_survfit.R

@@ -36,10 +36,10 @@
 #' library(survival)
 #' library(ggsurvfit)
 #'
-#' survfit(Surv_CNSR(AVAL, CNSR) ~ TRTA, cards::ADTTE) |>
+#' survfit(Surv_CNSR(AVAL, CNSR) ~ TRTA, data = cards::ADTTE) |>
 #'   ard_survival_survfit(times = c(60, 180))
 #'
-#' survfit(Surv_CNSR(AVAL, CNSR) ~ TRTA, cards::ADTTE) |>
+#' survfit(Surv_CNSR(AVAL, CNSR) ~ TRTA, data = cards::ADTTE, conf.int = 0.90) |>
 #'   ard_survival_survfit(probs = c(0.25, 0.5, 0.75))
 #'
 #' # Competing Risks Example ---------------------------