add error policy to CONTRIBUTING.md

Author: Shoshana Berleant

CONTRIBUTING.md

@@ -10,10 +10,16 @@
 * Pull Requests should be tested, if feasible:
     - bugfixes should include regression tests
     - new behavior should at least get minimal exercise
-* Use a descriptive prefix for your PR: ENH, FIX, TST, DOC, STY, REF (refactor), WIP (Work in progress)
-* After submiting the PR, include an update to the CHANGES file: prefix: description (URL of pull request)
+* Use a descriptive prefix for your PR: ENH (enhancement), FIX, TST, DOC, STY, REF (refactor), WIP (Work in progress)
+* After submitting the PR, include an update to the CHANGES file: prefix: description (URL of pull request)
 * `make specs`
 * do: `make check-before-commit` before submitting the PR. This will require you to either install or be in developer mode with: `python setup.py install/develop`.
+* In general, do not catch exceptions without good reason. 
+  * catching non-fatal exceptions. 
+    Log the exception as a warning.
+  * adding more information about what may have caused the error.
+    Raise a new exception using ``raise_from(NewException("message"), oldException)`` from ``future``.
+    Do not log this, as it creates redundant/confusing logs.
 
 ## Contributing issues