Update R.gitignore

Made _freeze directory exclusion optional

R.gitignore

@@ -20,6 +20,7 @@
 
 # RStudio files
 .Rproj.user/
+.Rbuildignore
 
 # produced vignettes
 vignettes/*.html
@@ -28,7 +29,7 @@ vignettes/*.pdf
 # OAuth2 token, see https://github.com/hadley/httr/releases/tag/v0.3
 .httr-oauth
 
-# knitr and R markdown default cache directories
+# Quarto, knitr and R markdown default cache directories
 *_cache/
 /cache/
 
@@ -62,4 +63,6 @@ renv/
 /_extensions/
 /_*.local
 
-/_freeze/
+# **Optional**
+# Depends on if you need others to reproduce your computational environment (https://quarto.org/docs/projects/code-execution.html#using-freeze)
+#/_freeze/