Improve font size documentation (#3787)

* updating font size units for #3458

* making an update with correct read lines setting

* adding the font size units in issue #3258

* incorporate edit suggestion by @thomasp85.

Co-authored-by: Claus Wilke <wilke@austin.utexas.edu>

Author: melimore86

R/theme-defaults.r

@@ -4,7 +4,7 @@
 #' [theme()] if you just need to tweak the display of an existing
 #' theme.
 #'
-#' @param base_size base font size
+#' @param base_size base font size, given in pts.
 #' @param base_family base font family
 #' @param base_line_size base size for line elements
 #' @param base_rect_size base size for rect elements