Added a better exception when a token is missing

spring-cloud-release-tools-core/src/main/java/org/springframework/cloud/release/internal/git/GithubMilestones.java

@@ -45,7 +45,10 @@ class GithubMilestones {
 
 	void closeMilestone(ProjectVersion version) {
 		Assert.hasText(this.properties.getGit().getOauthToken(),
-				"You have to pass Github OAuth token for milestone closing to be operational");
+				"You must set the value of the OAuth token. You can do it "
+						+ "either via the command line [--releaser.git.oauth-token=...] "
+						+ "or put it as an env variable in [~/.bashrc] or "
+						+ "[~/.zshrc] e.g. [export RELEASER_GIT_OAUTH_TOKEN=...]");
 		String tagVersion = version.version;
 		Milestone.Smart foundMilestone = matchingMilestone(tagVersion, openMilestones(version));
 		if (foundMilestone != null) {

spring-cloud-release-tools-core/src/test/java/org/springframework/cloud/release/internal/git/GithubMilestonesTests.java

@@ -229,7 +229,7 @@ public class GithubMilestonesTests {
 
 		thenThrownBy(() -> milestones.closeMilestone(nonGaSleuthProject()))
 				.isInstanceOf(IllegalArgumentException.class)
-				.hasMessageContaining("You have to pass Github OAuth token for milestone closing to be operational");
+				.hasMessageContaining("You must set the value of the OAuth token");
 	}
 
 	ReleaserProperties withToken() {