docs: add comments of workable code

String/CheckPangram.js

@@ -9,6 +9,14 @@ const checkPangram = (string) => {
  throw new TypeError('The given value is not a string')
  }
 
+ /**
+ * match all 26 alphabets using regex, with the help of: 
+ * Capturing Group
+ * Character set
+ * Negative lookahead
+ * Dot & star
+ * Numeric reference
+ */
  return string.match(/([a-z])(?!.*\1)/gi).length === 26
 }