Add missing pluralisation

tcharding · tcharding · commit 3a31191cf493 · 2021-08-30T11:24:08.000+10:00
As for the subsequent usage 'number' should be pluralised.
diff --git a/12_2_Using_Other_Script_Commands.md b/12_2_Using_Other_Script_Commands.md
@@ -18,7 +18,7 @@ Manipulate one number:
 
 Also see: `OP_0NOTEQUAL` (0x92)
 
-Manipulate two number mathematically:
+Manipulate two numbers mathematically:
 
 * OP_ADD (0x93) — Add two numbers
 * OP_SUB (0x94) — Subtract two numbers
