docs: add kubernetes (#33)

- Update PR template to use Go language conventions.
- Moved healthcheck middleware to hijack a request before logging.
- Rewrote the quickstart guides to follow a similar pattern.
- Added an overview blurb on pomerium and its goals.
- Add an "example config" section to docs.

.github/PULL_REQUEST_TEMPLATE

@@ -1,12 +1,24 @@
-<!--  Thanks for sending a pull request!  Here are some tips for you:
-1. If this PR closes another issue, add 'closes #<issue number>' somewhere in the PR summary. GitHub will automatically close that issue when this PR gets merged. Alternatively, adding 'refs #<issue number>' will not close the issue, but help provide the reviewer more context.-->
-2. The PR title is formatted as follows: `proxy: frob the quux before blarfing`
+<!--  Thanks for sending a pull request!
+We generally follow Go coding and contributing conventions 
+which you can read about here https://golang.org/doc/contribute.html#commit_messages
 
-**What this PR does / why we need it**:
+Here's an example of a good PR/Commit:
 
-**Special notes for your reviewer**:
+    math: improve Sin, Cos and Tan precision for very large arguments
 
-**If applicable**:
-- [ ] this PR contains documentation
-- [ ] this PR contains unit tests
-- [ ] this PR has been tested for backwards compatibility
+    The existing implementation has poor numerical properties for
+    large arguments, so use the McGillicutty algorithm to improve
+    accuracy above 1e10.
+
+    The algorithm is described at https://wikipedia.org/wiki/McGillicutty_Algorithm
+
+    Fixes #159
+-->
+
+
+<!--  handy checklist ; not required--> 
+**Checklist**:
+- [ ] documentation updated
+- [ ] unit tests added
+- [ ] related issues referenced
+- [ ] ready for review