message: Add build parameter descriptions .
diff: @@ -18,8 +18,10 @@ pipeline {
  disableConcurrentBuilds()
  }
  parameters {
  - string(defaultValue: '', name: 'stan_pr')
  - string(defaultValue: '', name: 'math_pr')
  + string(defaultValue: '', name: 'stan_pr',
  + description: "Stan PR to test against. Will check out this PR in the downstream Stan repo.")
  + string(defaultValue: '', name: 'math_pr',
  + description: "Math PR to test against. Will check out this PR in the downstream Math repo.")
  }
  stages {
  stage('Clean & Setup') {
  