docs: mention --read-only for spell-check in vignettes

vignettes/available-hooks.Rmd

@@ -196,6 +196,14 @@ The `lang` arg will be passed to `spelling::spell_check_files()`.
       id: spell-check
       args: [--lang=<language>]
 
+**read only**
+
+The `--read-only` flag will be passed to spell check. This flag makes
+this hook idempotent.
+
+      id: spell-check
+      args: [--read-only]
+
 This hook does not modify input files. It will add all words not found
 in the dictionary to `inst/WORDLIST`, assuming they were spelled
 correctly but were not in the dictionary. An example might be "RStudio".
@@ -205,6 +213,8 @@ them and remove them from `inst/WORDLIST`. If there were not typos, or
 you fixed all, stage `inst/WORDLIST` and this time, the commit should
 pass.
 
+To opt out of updating `inst/WORDLIST` provide the `--read-only` flag.
+
 ## `roxygenize`
 
 A hook to run `roxygen2::roxygenize()`. Makes sure you commit your `.Rd`

vignettes/hook-order.Rmd

@@ -29,7 +29,7 @@ Read only hooks should generally run only after write hooks.
 -   roxygenize - caches
 -   codemeta-description-updated - must be before use-tidy-description
 -   use-tidy-description
--   spell-check - updates `inst/WORDLIST`; should run after roxygenize
+-   spell-check - updates `inst/WORDLIST` (unless `--read-only` arg is specified); should run after roxygenize
 
 ### Read only