Clarify test comment

Co-Authored-By: Michael Chirico <chiricom@google.com>

Author: aitap

inst/tests/tests.Rraw

@@ -21670,7 +21670,8 @@ test(2375.4, print(data.table(x="abcdefghijklmnopqrstuvwxyz")), output="abcdefgh
 test(2375.5, print(data.table(id=1L, score=99.1, txt="abcdefghijklmnopqrstuvwxyz")), output="abcdefghijklmn...", options=list(width=20, datatable.prettyprint.char=NULL))
 test(2375.6, print(data.table(x=rep("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 1e6)), topn=1), output="1000000: ABCDEFGHIJKLM...", options=list(width=25, datatable.prettyprint.char=NULL))
 
-# rbindlist() used to put O(ncol(...)) > R_PPStackSize = 50000 items on the protect stack, #7793
+# rbindlist() used to put O(ncol(...)) > R_PPStackSize items on the protect stack, #7793
+# Assuming 50000 as the default protection stack size, although R --max-ppsize=... can increase it to 500000.
 x = as.data.table(as.list(1:50001))
 test(2376, rbindlist(list(x)), x)
 rm(x)