Add notes about Travis usage

.travis.yml

@@ -3,6 +3,8 @@
 # After changing this file, check it on:
 #   http://lint.travis-ci.org/
 
+# See docs/travis_notes.txt for some guidelines
+
 language: python
 
 python:

doc/travis_notes.txt

@@ -0,0 +1,20 @@
+
+
+Travis Notes:
+
+- Use http://lint.travis-ci.org/ to make sure it is valid yaml.
+- Make sure all of your "-" lines start on the same column
+- Make sure all of your "if" lines are aligned with the "else" and "fi" lines
+- "If" blocks must be on one travis statement and have semicolons at the end of each line:
+
+```
+    - if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; then
+        echo "2.7";
+      else
+        echo "Not 2.7";
+      end
+```
+
+- "If" blocks cannot contain comments
+- Use `travis_retry` before a command to have it try several times before failing
+  (useful for installing from third party sources)