[README.md] Add is_live, start_time and end_time to output template section (closes #14926)

README.md

@@ -511,6 +511,9 @@ The basic usage is not to set any template arguments when downloading a single f
  - `average_rating` (numeric): Average rating give by users, the scale used depends on the webpage
  - `comment_count` (numeric): Number of comments on the video
  - `age_limit` (numeric): Age restriction for the video (years)
+ - `is_live` (boolean): Whether this video is a live stream or a fixed-length video
+ - `start_time` (numeric): Time in seconds where the reproduction should start, as specified in the URL
+ - `end_time` (numeric): Time in seconds where the reproduction should end, as specified in the URL
  - `format` (string): A human-readable description of the format 
  - `format_id` (string): Format code specified by `--format`
  - `format_note` (string): Additional info about the format