Clarify optional Shardok roll argument (#8439)

docs/TEXT_CLIENT_OPERATOR_GUIDE.md

@@ -100,10 +100,23 @@ Post one of the currently listed command indices with:
 post-shardok <index>
 ```
 
+Omit the optional roll value during normal play. The server then generates any
+roll required by the selected command. To override that roll for deterministic
+testing, append an integer value:
+
+```text
+post-shardok <index> <integer-roll>
+```
+
+`roll` is a placeholder in command usage, not a literal argument. Only an
+integer is accepted, and the override has an effect only for Shardok commands
+that support a client-supplied roll.
+
 For a specific active battle:
 
 ```text
 post-shardok <shardok-game-id> <index>
+post-shardok <shardok-game-id> <index> <integer-roll>
 ```
 
 Use `shardok-commands-json` or `shardok-units-json` when the concise output omits a needed field.