Add CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,16 @@
+# Contributing
+
+* Please keep the scope of this project in mind. Dutyl is about tool integration
+- if your contribution is not using D tools, and can be run on a machine that
+doesn't have any of the D tools installed, it's probably not a good fit for
+Dutyl, and you should try sending it to
+[the d.vim plugin](https://github.com/JesseKPhillips/d.vim) instead.
+For example, syntax highlighting based on Vim regular syntax highlighting
+facilities doesn't belong here, but syntax highlighting based on some tool that
+uses libdparse or something it might be a good fit.
+
+* At the beginning of `doc/dutyl.txt` there is a line that specifies the
+  current version of Dutyl. When there are changes in the code but a new
+  version is not yet released, there should be a `+` after the version - e.g.
+  `Version: 1.2.3+` - to indicate that this is a different, mid-version. If
+  that `+` is not there already, please add it as part of the PR.

README.md

@@ -76,3 +76,7 @@ let g:dutyl_tagsFileName='newnamefortagsfile'
 ```
 Note that the new tags file name will still have to be in `tags` in order
 for Vim to recognize it.
+
+## Contributing
+
+Please see [CONTRIBUTING.md](CONTRIBUTING.md).