Updating the contribution doc. (#275)

CONTRIBUTING.md

@@ -1,27 +1,38 @@
-Want to contribute? Great! First, read this page (including the small print at the end).
-
-### Before you contribute
-
-Before we can use your code, you must sign the
-[Google Individual Contributor License Agreement](https://cla.developers.google.com/about/google-individual)
-(CLA), which you can do online. The CLA is necessary mainly because you own the
-copyright to your changes, even after your contribution becomes part of our
-codebase, so we need your permission to use and distribute your code. We also
-need to be sure of various other things—for instance that you'll tell us if you
-know that your code infringes on other people's patents. You don't have to sign
-the CLA until after you've submitted your code for review and a member has
-approved it, but you must do it before we can put your code into our codebase.
-Before you start working on a larger contribution, you should get in touch with
-us first through the issue tracker with your idea so that we can help out and
-possibly guide you. Coordinating up front makes it much easier to avoid
-frustration later on.
-
-### Code reviews
-
-All submissions, including submissions by project members, require review.  
+Want to contribute? Great: read the page (including the small print at the end).
+
+# Before you contribute
+
+As an individual, sign the [Google Individual Contributor License
+Agreement](https://cla.developers.google.com/about/google-individual) (CLA)
+online. This is required for any of your code to be accepted.
+
+Before you start working on a larger contribution, get in touch with us first
+through the issue tracker with your idea so that we can help out and possibly
+guide you. Coordinating up front makes it much easier to avoid frustration later
+on.
+
+# Code reviews
+
+All submissions, including submissions by project members, require review.
 We use Github pull requests for this purpose.
 
-### The small print
+The pprof source code is in Go with a bit of JavaScript, CSS and HTML. If you
+are new to Go, read [Effective Go](https://golang.org/doc/effective_go.html) and
+the [summary on typical comments during Go code
+reviews](https://github.com/golang/go/wiki/CodeReviewComments).
+
+Cover all new functionality with tests. Enable Travis on your forked repo,
+enable builds of branches and make sure Travis is happily green for the branch
+with your changes.
+
+The code coverage is measured for each pull request. The code coverage is
+expected to go up with every change.
+
+Pull requests not meeting the above guidelines will get less attention than good
+ones, so make sure your submissions are high quality.
+
+# The small print
 
-Contributions made by corporations are covered by a different agreement than the one above,  
-the [Software Grant and Corporate Contributor License Agreement](https://cla.developers.google.com/about/google-corporate).
+Contributions made by corporations are covered by a different agreement than the
+one above, the [Software Grant and Corporate Contributor License
+Agreement](https://cla.developers.google.com/about/google-corporate).