Document the missing dependency for pegdown

[odupuy]

Thanks for raising a Swagger2Markup issue. Please provide a brief description of your problem along with the Swagger2Markup version you are using. If possible, please also consider putting together a complete Swagger specification that reproduces the issue. It's better if the Swagger specification is small and isolate the issue.

Swagger2Markup version: 1.3.3

Problem description: Missing dependencies when following the maven instructions. I have added swagger2markup to my pom.xml. I then test this example and I end up with this error already reported. I have not tested Gradle.

Fix: Simply list pegdown in the dependencies for Gradle and Maven (or make it part of the Swagger2Markup dependencies?)

        <dependency>
            <groupId>org.pegdown</groupId>
            <artifactId>pegdown</artifactId>
            <version>1.6.0</version>
            <scope>runtime</scope>
        </dependency>