docs: improve 'usage' section

README.md

@@ -18,22 +18,42 @@ npm install wisely
 
 ## Usage
 
+### Obscures the entire text
+
 ```js
 import wisely from 'wisely';
 
 const text = 'Palestine will be free! Freedom is the right of ALL nations!';
 
-// Obscuring the whole text
-const res1 = wisely({ text });
+console.log(wisely({ text }));
+// P@l3$t|n3 w!ll 83 fr33! Fr33d0m |$ t#3 r!6#t 0f @LL n4t|0n5!
+```
 
-// Only obscures the specified phrases
-const res2 = wisely({ text, phrases: ['palestine', 'free'] });
+### Obscures certain phrases
 
-console.log(res1, res2);
-// P@l3$t|n3 w!ll 83 fr33! Fr33d0m |$ t#3 r!6#t 0f @LL n4t|0n5!
+```js
+console.log(wisely({ text, phrases: ['palestine', 'free'] }));
 // P4l35t1n3 will be fr33! Freedom is the right of ALL nations!
 ```
 
+### Obscures with custom character set
+
+```js
+const customCharSet = {
+  a: ['@', '4'],
+  e: ['3'],
+  i: ['1', '!'],
+  o: ['0'],
+  s: ['5', '$'],
+  t: ['7'],
+};
+
+console.log(wisely({ text, charSets: [customCharSet] }));
+// P@l3$7!n3 w1ll b3 fr33! Fr33d0m 1$ 7h3 r1gh7 0f 4LL n@710n$!
+```
+
+> See [`options.charsets`](#charsets) for more details.
+
 ## API
 
 ### `wisely(options)`