Add info about shellcheck --shell=

SC2148.md

@@ -1,5 +1,12 @@
 Add shebang to the top of your script:
 
-``
+```bash
 #!/bin/bash
-``
+```
+
+Alternatively, if that is not possible / desirable, you can use the `--shell` switch:
+```bash
+shellcheck --shell=bash without-shebang.sh
+```
+
+See `shellcheck --help` for a list of supported flavors.