Add documentation on how to build from source

I’m interested in using the new functionality for signing MSI files, specifically the Gradle plugin. But since version 3.0 hasn’t been released yet (and there’s no 3.0-SNAPSHOT or similar available in public repos), I’ll have to build from source.

Unfortunately, I’m having trouble figuring out how. I’m not very familiar with Maven, so I’m unsure of the proper way to do this. I don’t see any sort of wrapper, so I installed the latest version of Maven, and tried running mvn compile, but it didn’t seem to produce a Gradle plugin. I tried going to jsign-gradle-plugin and running gradle build (again, no wrapper) and got the following error:

> Could not resolve all files for configuration ':compileClasspath'.
   > Could not find net.jsign:jsign-core:2.0.
     Searched in the following locations:
       - file:/~/.m2/repository/net/jsign/jsign-core/2.0/jsign-core-2.0.pom
     If the artifact you are trying to retrieve can be found in the repository but without metadata in 'Maven POM' format, you need to adjust the 'metadataSources { ... }' of the repository declaration.
     Required by:
         project :

I assume I’m doing something wrong, but I have no idea what. If directions on building from source could be added to either the readme or to a separate file in the root project, I would appreciate it.

[ebourg]

@Thunderforge the version 3.0 has just been released.

[ebourg]

Building with Maven is just a matter of typing mvn package -DskipTests at the root of the project, not in the plugin directory. You’ll need jsign-core-3.0-SNAPSHOT.jar and jsign-gradle-plugin-3.0-SNAPSHOT.jar on the classpath to use the plugin.