Update README and comments

Author: DivineOmega

README.md

@@ -12,4 +12,42 @@ composer require divineomega/php-wikitext-parser
 
 ## Usage
 
-TODO
+The most basic usage is to convert a Wikitext formatted
+string to plain text.
+
+```php
+$plainText = (new WikitextParser())
+    ->setWikitext($wikitext)
+    ->parse();
+```
+
+### Alternative Format
+
+You are also able to specify alternative formats to 
+convert to, using the `setFormat` method. By default, 
+this is set to plain text.
+
+For example, you can convert Wikitext to HTML, as shown
+below.
+
+```php
+$plainText = (new WikitextParser())
+    ->setWikitext($wikitext)
+    ->setFormat(Format::HTML)
+    ->parse();
+```
+
+### Caching
+
+By default, file caching is used. If you wish, you can
+specify any PSR-6 compliant caching library. This is
+done using the `setCache` method as should below.
+
+```php
+$cache = new OtherPsr6CacheItemPool();
+
+$plainText = (new WikitextParser())
+    ->setCache($cache)
+    ->setWikitext($wikitext)
+    ->parse();
+```

src/Parser.php

@@ -26,12 +26,24 @@ public function __construct()
         $this->setCache($cacheItemPool);
     }
 
+    /**
+     * Set an alternative PSR-6 compliant cache item pool.
+     *
+     * @param CacheItemPoolInterface $cacheItemPool
+     * @return $this
+     */
     public function setCache(CacheItemPoolInterface $cacheItemPool)
     {
         $this->cache = $cacheItemPool;
         return $this;
     }
 
+    /**
+     * Set the Wikitext to parse.
+     *
+     * @param string $wikitext
+     * @return Parser
+     */
     public function setWikitext(string $wikitext) : Parser
     {
         $this->wikitext = $wikitext;
@@ -52,6 +64,11 @@ public function setFormat(string $format = Format::PLAIN_TEXT) : Parser
         return $this;
     }
 
+    /**
+     * Constructs the Wikitext parser URL.
+     *
+     * @return string
+     */
     private function buildUrl()
     {
         return $this->endpoint.$this->queryString.urlencode($this->wikitext);