title: How to trigger bitbucket pipeline in multibranch
body: <p>I have a single repository under bit-bucket account and this repository has this 4 branches :</p>
  
  <pre><code>- master 
  - API
  - Admin
  - Web
  </code></pre>
  
  <p>and I have only one <code>bitbucket-pipelines.yml</code> under <code>master branch</code> and its like that :</p>
  
  <pre><code>image: maven:3.5.0-jdk-7
  
  pipelines:
    branches:
      API:
       - step:
          caches:
            - maven
          script: 
  
             - mvn install
  </code></pre>
  
  <p>so I expect that whenever any push happened to API branch will trigger this pipeline, bit in fact it didn't happen unless the push is done to the master branch, the only way out is to put this same file also under API branch as well, although the doc says its only one copy located under repo root <code>master branch</code>, So how can I achieve that plz?</p>
  
  <p>and if I need to put same pipeline file in all branches I see it completely ridicules, so can any one plz clarify that? 
  Thanks in advance! </p>