Merge branch 'erodrigu-README-file' into '2018-patches'

Added a README file to the project

See merge request lhcb/DaVinci!206

README.md

+# General information
+
+The project contains several active and maintained branches, such as the `201X-patches` branches.
+They are all protected, meaning that code cannot be pushed into them directly but only through merge requests (MRs).
+This helps with the validation of code prior to making it available in the official branches for future releases.
+
+## Where to commit code to
+
+- Bug fixes for 2018 data-taking should be committed as MRs to `2018-patches`. They will then be propagated to the
+`run2-patches` branch  (and master if appropriate) by the applications managers.
+
+- Any other changes for Run 1 and Run 2 analysis (or re-reconstruction, re-stripping) should go to the `run2-patches` branch.
+  They will then be propagated to `master (if relevant also for Upgrade) by the applications managers.
+
+- Any changes specific to Upgrade should *only* got to `master`.
+
+-  Things may be different for bug fixes to old and/or specific versions of DaVinci, in which case it is probably best to discuss 
+unless you know exactly what you are doing.
+
+In doubt, please get in touch before creating a MR.