add docs for categories

docs/README.md

@@ -4,6 +4,7 @@ Welcome to the documentation for Photowall API 2.
 
 ## Resources
 
+* [Categories](categories.md)
 * [Prices](prices.md)
 
 ## Authentication

docs/categories.md

@@ -0,0 +1,19 @@
+# Categories
+
+## List categories
+
+```
+curl -X GET https://api2.photowall.com/categories/
+```
+
+## Show category
+
+```
+curl -X GET https://api2.photowall.com/categories/1
+```
+
+## Update category
+
+```
+curl -X PUT https://api2.photowall.com/categories/1 -H "Content-Type: application/json" -d '{"name": "Dogs"}'
+```