DOC: add release-procedure.md to main dir

Author: jreback

release-procedure.md

@@ -0,0 +1,18 @@
+*   Tag commit
+
+        git tag -a x.x.x -m 'Version x.x.x'
+
+*   and push to github
+
+        git push pandas-datareader master --tags
+
+*  Upload to PyPI
+
+        git clean -xfd
+        python setup.py register sdist bdist_wheel --universal
+        twine upload dist/*
+
+*  Do a pull-request to the feedstock on `pandas-datareader-feedstock <https://github.com/conda-forge/pandas-datareader-feedstock/>`__
+
+        update the version
+        update the SHA256 (retrieve from PyPI)