Provide default value for ossrhUsername so build doesn't break

Added instructions how to setup deployment

Author: mrotteveel

devdoc/deploy.md

@@ -4,5 +4,26 @@ Deploying
 To deploy to Maven use
 
 ```
-gradlew uploadArchives -PcredentialsPassphrase=<password>
+gradlew uploadArchives -PcredentialsPassphrase=<credentials password>
+```
+
+Where `<credentials password>` is the password used to add the credentials (see 
+also below).
+
+To be able to deploy, you need the following:
+
+a `<homedir>/.gradle/gradle.properties` with the following properties:
+
+```
+signing.keyId=<gpg key id>
+signing.secretKeyRingFile=<path to your secring.gpg> 
+
+ossrhUsername=<sonatype OSSRH username>
+```
+
+In addition, you need to set the following credentials
+
+```
+./gradlew addCredentials --key signing.password --value <your secret key password> -PcredentialsPassphrase=<credentials password> 
+./gradlew addCredentials --key ossrhPassword --value <your sonatyp OSSRH password> -PcredentialsPassphrase=<credentials password> 
 ```

gradle.properties

@@ -0,0 +1,2 @@
+# Default value so the build script doesn't break
+ossrhUsername=don't break the build