Add new Rows which sums & counts values

tidyverse
3 
library(tidyverse)

(raw1 <- tribble(~Month,~Date,~Day,~Mins,~Calories,~Type,
  "March",16,"Monday","00:12:20",NA,"Running",
  "March",17,"Tuesday","00:44:11",140,"Strength",
  "March",19,"Thursday","00:15:42",NA,"Running",
  "April",2, "Thursday","00:43:13",140,"Strength",
  "April",5, "Sunday","00:30:00,65",NA,"Core",
  "April",6, "Monday","00:30:09,90",NA,"Cardio") %>%
    mutate(Month=as_factor(Month)))

(smry2 <- group_by(raw1,
                   Month) %>% summarise(
                     days=length(unique(Date)),
                     calorie_sum = sum(Calories,na.rm = TRUE)
                   ))
empty_raw <- slice(raw1, 1) %>%
  select(-Month) %>%
  mutate_all(.funs = function(x) {
    y <- NA
    class(y) <- class(x)
    y
  })

  (smry3 <- expand_grid(smry2,empty_raw))

(to_display <- bind_rows(raw1,smry3) %>% arrange(Month,Date))