Add coveralls link to README.md and a note on testing in CONTRIBUTING

based on #9493.

CONTRIBUTING.md

@@ -44,6 +44,18 @@ Julia has a built-in [package manager](https://github.com/JuliaLang/METADATA.jl)
 
 For developers who need to wrap C libraries so that they can be called from Julia, the [Clang.jl](https://github.com/ihnorton/Clang.jl) package can help generate the wrappers automatically from the C header files.
 
+### Writing tests
+
+There are never enough tests. Track [code coverage at Coveralls](https://coveralls.io/r/JuliaLang/julia), and help improve it.
+
+1. Go visit https://coveralls.io/r/JuliaLang/julia.
+
+2. Browse through the source files and find some untested functionality (highlighted in red) that you think you might be able to write a test for.
+
+3. Write a test that exercises this functionality---you can add your test to one of the existing files, or start a new one, whichever seems most appropriate to you. If you're adding a new test file, make sure you include it in the list of tests in `test/runtests.jl`. http:https://julia.readthedocs.org/en/latest/stdlib/test/ may be helpful in explaining how the testing infrastructure works. Submit the test as a pull request (see [CONTRIBUTING.md](https://github.com/JuliaLang/julia/blob/master/CONTRIBUTING.md)).
+
+[Issue 9493](https://github.com/JuliaLang/julia/issues/9493) has a more detailed discussion on code coverage.
+
 ### Improving documentation
 
 *By contributing documentation to Julia, you are agreeing to release it under the [MIT License](https://github.com/JuliaLang/julia/tree/master/LICENSE.md).*
@@ -103,7 +115,9 @@ or with the `runtests.jl` script, e.g. to run `test/bitarray.jl` and `test/math.
 
 Make sure that [Travis](http:https://www.travis-ci.org) greenlights the pull request with a [`Good to merge` message](http:https://blog.travis-ci.com/2012-09-04-pull-requests-just-got-even-more-awesome/).
 
-##### General Formatting Guidelines For Julia code contributions
+### Code Formatting Guidelines
+
+#### General Formatting Guidelines for Julia code contributions
 
  - 4 spaces per indentation level, no tabs
  - use whitespace to make the code more readable
@@ -113,7 +127,7 @@ Make sure that [Travis](http:https://www.travis-ci.org) greenlights the pull request w
  - use upper camel case convention for modules, type names
  - use lower case with underscores for method names
 
-##### General Formatting Guidelines For C code contributions
+#### General Formatting Guidelines For C code contributions
 
  - 4 spaces per indentation level, no tabs
  - space between if and ( (if (x) ...)
@@ -123,7 +137,7 @@ Make sure that [Travis](http:https://www.travis-ci.org) greenlights the pull request w
  - if one part of an if..else chain uses { } then all should
  - no whitespace at the end of a line
 
-##### Git Recommendations For Pull Requests
+### Git Recommendations For Pull Requests
 
  - Avoid working from the `master` branch of your fork, creating a new branch will make it easier if Julia's `master` changes and you need to update your pull request.
  - Try to [squash](http:https://gitready.com/advanced/2009/02/10/squashing-commits-with-rebase.html) together small commits that make repeated changes to the same section of code so your pull request is easier to review, and Julia's history won't have any broken intermediate commits. A reasonable number of separate well-factored commits is fine, especially for larger changes.
@@ -153,8 +167,8 @@ While getting familiar with Julia, remember to check out [the docs](http:https://docs.
  - **Source code:** <https://github.com/JuliaLang/julia>
  - **Git clone URL:** <git:https://github.com/JuliaLang/julia.git>
  - **Documentation:** <http:https://julialang.org/manual/>
- - **CodeSpeed:** <http:https://speed.julialang.org>
- - **Status:** <http:https://status.julialang.org>
+ - **Status: ** <http:https://status.julialang.org/>
+ - **Code coverage:** <https:https://coveralls.io/r/JuliaLang/julia>
 
 * Design of Julia
  - [Julia: A Fast Dynamic Language for Technical Computing](http:https://julialang.org/images/julia-dynamic-2012-tr.pdf)

README.md

@@ -27,6 +27,7 @@ This is the GitHub repository of Julia source code, including instructions for c
 - **Git clone URL:** <git:https://github.com/JuliaLang/julia.git>
 - **Mailing lists:** <http:https://julialang.org/community/>
 - **IRC:** <http:https://webchat.freenode.net/?channels=julia>
+- **Code coverage:** <https://coveralls.io/r/JuliaLang/julia>
 
 The mailing list for developer discussion is
 <http:https://groups.google.com/group/julia-dev/>. All are welcome, but the volume