DOC: put contribution guidelines in CONTRIBUTING.md

Author: y-p

CONTRIBUTING.md

@@ -1 +1,35 @@
-Please see [Developers](http://pandas.pydata.org/developers.html) page on the project website.
+Guidelines
+---
+
+All contributions, bug reports, bug fixes, documentation improvments,
+enhancements and ideas are welcome. Please try and follow these guidelines
+as best you can, this makes it easier for us to accept your contribution or
+address the issue you're having.
+
+- When submitting a bug report:
+  - Please include a short, self-contained python snippet.
+  - Specify the pandas version used. (you can check `pandas.__version__`).
+  - Explain what the expected behavior was, and what you saw instead.
+- When submitting a Pull Request
+  - **Make sure the test suite passes**., and that means on python3 as well.
+    You can use "test_fast.sh", or tox locally and/or enable Travis-CI on you're fork.
+  - We suggest you enable Travis-CI on your fork, to make it easier for the team
+     to see that the PR does indeed pass all the tests.
+  - Pandas cares about performance, you can use the included "test_perf.sh"
+    script to make sure your PR does not introduce any performance regressions
+    in the library.
+  - **Don't** merge upstream into a branch you're going to submit as a PR,
+    This can create all sorts of problems. Use "git rebase" instead. This ensures
+    no merge conflicts occur when you're code is merged by the core team.
+  - An informal commit message format is in use by the project, please try
+    and adhere to it. Use a "ENH: ", "TST:", "BUG:", "DOC:", etc' prefix in
+    your commit title. Check the output of "git log" for examples.
+  - doc/source/vx.y.z.txt contains an on-going change-log for the version under
+    development, look at previous versions, and add an entry as needed in
+    a separate commit in your PR.
+  - For extra brownie points, use "git rebase -i" to squash and reorder
+    commits in your PR so that the history makes the most sense. Use your own
+    judgment to decide what history needs to be preserved.
+
+Please see [Developers](http://pandas.pydata.org/developers.html) page on
+the project website for more details.