Merge remote-tracking branch 'upstream/master' into 0.15-whats-new

* upstream/master:
  setuptools-scm (3) (pydata#3724)
  Fix Sphinx links on contributing doc page (pydata#3710)

Author: dcherian

doc/contributing.rst

@@ -231,9 +231,9 @@ About the *xarray* documentation
 --------------------------------
 
 The documentation is written in **reStructuredText**, which is almost like writing
-in plain English, and built using `Sphinx <http://sphinx.pocoo.org/>`__. The
+in plain English, and built using `Sphinx <http://sphinx-doc.org/>`__. The
 Sphinx Documentation has an excellent `introduction to reST
-<http://sphinx.pocoo.org/rest.html>`__. Review the Sphinx docs to perform more
+<http://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html>`__. Review the Sphinx docs to perform more
 complex changes to the documentation as well.
 
 Some other important things to know about the docs:

requirements.txt

@@ -0,0 +1,6 @@
+# This file is redundant with setup.cfg;
+# it exists to let GitHub build the repository dependency graph
+# https://help.github.com/en/github/visualizing-repository-data-with-graphs/listing-the-packages-that-a-repository-depends-on
+
+numpy >= 1.15
+pandas >= 0.25