add roadmap to project. Closes #29

ROADMAP.md

+# ROADMAP
+
+## Project mission and summary
+
+Welcome to the rostools project! 
+
+Our dream is a future where the default for science is to be reproducible and
+open. We hope that one day, researchers will conduct their scientific activities
+following open scientific principles not as an active choice but because it is
+the proper and *easier* way of doing science.
+
+To acheive our dream, our mission is to create a highly opinionated, practical,
+and process-oriented manifesto and an accompanying ecosystem of software tools,
+documentation, tutorials, and learning materials, supported by a network of
+practitioners (researchers), that informs researchers on how to conduct open and
+reproducible science.
+
+See the [overview](index.Rmd) for more description about the project's vision and mission.
+If you are interested in getting involved,
+check out our [contributing guidelines](CONTRIBUTING.md) for more details.
+
+## Milestones and tasks
+
+Our main priority is to finish the **first working version** of the manifesto.
+All tasks related to completing our milestones are listed in GitLab Issues and 
+can be viewed on the [Issue Board](https://gitlab.com/rostools/manifesto/-/boards).
+Issues labeled with [`Priority: High`](https://gitlab.com/rostools/manifesto/issues?label_name%5B%5D=Priority%3A+High)
+or with [`Content`](https://gitlab.com/rostools/manifesto/issues?scope=all&utf8=%E2%9C%93&state=opened&label_name[]=Content)
+are good issues to work on if they aren't already assigned.