docs: add command-v example pair

examples/standards/11-command-v-not-which.bad.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+#
+# BAD: which is an external program with non-portable output and unreliable
+# exit status. Prefer the shell builtin `command -v`.
+# expect-shellcheck: SC2230
+if which jq > /dev/null 2>&1; then
+  printf 'jq is available\n'
+else
+  printf 'jq is not available\n'
+fi

examples/standards/11-command-v-not-which.good.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+#
+# GOOD: command -v is a shell builtin with predictable output and exit status
+# for checking whether a command is available.
+set -euo pipefail
+
+main() {
+  if command -v jq > /dev/null; then
+    printf 'jq is available\n'
+  else
+    printf 'jq is not available\n'
+  fi
+}
+
+main "$@"

examples/standards/README.md

@@ -30,6 +30,7 @@ paired files side by side.
 | `08-brace-expansions` | `${base}_2026` | `$base_2026` (a different var) | `SC2250` |
 | `09-no-parse-ls` | glob `"$dir"/*.txt` | `$(ls *.txt)` | `SC2045` |
 | `10-parameter-expansion-not-sed` | `${path##*/}` strips in-process | `echo ... \| sed ...` forks twice | `SC2001` |
+| `11-command-v-not-which` | `command -v jq` checks a command | `which jq` is non-standard | `SC2230` |
 
 ## `.env.example`