Add capitalize docs

_filters/capitalize.md

@@ -0,0 +1,14 @@
+---
+title: capitalize
+---
+
+`capitalize` ensures the first character of your string is capitalized.
+
+{% highlight liquid %}
+{% raw %}
+{{ "title" | capitalize }}
+{% endraw %}
+# => "Title"
+{% endhighlight %}
+
+It only capitalizes the first character, so subsequent words will not be capitalized as well.