Add instructions for generating documentation from source

.travis.yml

@@ -5,3 +5,4 @@ script:
   - dub test --build=unittest --config=unittest
   - dub build --build=release --config=quickstartExample
   - dub build --build=release --config=qualifiersExample
+  - dub build --build=ddox

README.md

@@ -141,6 +141,14 @@ class BluePaint {
 ```
 If you registered multiple concrete types to the same supertype and you do not resolve using a qualifier, a ResolveException is thrown stating that there are multiple candidates for the type to be resolved.
 
+Documentation
+-------------
+You can generate Public API documentation from the source code using DUB:
+```
+dub build --build=ddox
+```
+The documentation can then be found in docs/
+
 Future Work
 -----------
 * Component scan (auto-registration)