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README.md

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 # bmad-ecosystem repository
 Bmad toolkit (library) for the simulation of charged particles and X-rays in accelerators and storage rings.
 
+**Bmad web site at: [https://www.classe.cornell.edu/bmad/](https://www.classe.cornell.edu/bmad/)**
+
+## Contributing to Bmad: Pull Requests
+
+What is a Pull Request? A Pull Request (PR) is a mechanism for requesting that changes that you have made 
+to a copy of this repository (bmad-sim/bmad-ecosystem) are integrated (merged) into this repository.
+
+The **main** branch of bmad-ecosystem is the central branch where all changes are merged into. 
+
+Pull Requests start with changes you have made to a branch that is not **main**. The PR is then a request for the changes you have made
+to be merged with **main**. 
+
+Your copy of the bmad-ecosystem repository can be a 
+[fork](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/about-forks)
+or simply a [clone](https://github.com/git-guides/git-clone).
+Note: The procedure for
+[creating a PR](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request) 
+when using a fork is somewhat different than when using a clone.