Change the Bitbucket pipeline config to trigger it manually

Edited README.md to include information on how to build the project using Bitbucket pipelines.
Moving to DONE.

PR is merged. I confirmed that when I merged the PR, no pipeline ran.
Ready for further testing.
To test, a developer could review the pipelines available and try running the new manual pipeline, which should work fine for developers not part of the core group.
Also, we should maybe now include some instructions explaining about how this works so that developers can build IGB in bitbucket using our Docker image.

Created the pull request: https://bitbucket.org/lorainelab/integrated-genome-browser/pull-requests/1022

Good idea, in my opinion! Please submit PR when ready.

I have made changes to include the manual build and I removed the default one, this would now allow the developer to push any number of commits to a branch and the jar doesn't build every time he pushes a commit but instead, it builds only when he runs the custom build manually. Here is the updated code: https://bitbucket.org/jaya-sravani/integrated-genome-browser/branch/IGBF-3771.