Clarify Revise and testing workflow (JuliaLang#35604)

* Clarify Revise and testing workflow

Co-authored-by: Stefan Karpinski <[email protected]>

Author: goretkin

CONTRIBUTING.md

@@ -201,11 +201,12 @@ Add new code to Julia's base libraries as follows (this is the "basic" approach;
 
 Build as usual, and do `make clean testall` to test your contribution. If your contribution includes changes to Makefiles or external dependencies, make sure you can build Julia from a clean tree using `git clean -fdx` or equivalent (be careful – this command will delete any files lying around that aren't checked into git).
 
-Note: You can run specific test files with `make`:
+#### Running specific tests
+There are `make` targets for running specific tests:
 
     make test-bitarray
 
-or with the `runtests.jl` script, e.g. to run `test/bitarray.jl` and `test/math.jl`:
+You can also use the `runtests.jl` script, e.g. to run `test/bitarray.jl` and `test/math.jl`:
 
     ./usr/bin/julia test/runtests.jl bitarray math
 
@@ -242,9 +243,9 @@ If you need to restart your Julia session, just start at step 2 above.
 built and incorporate them automatically. You only need to rebuild
 Julia if you made code-changes that Revise cannot handle.
 
-For convenience, there are also `test-revise-*` targets for every `test-*`
-target that use Revise to load any modifications to Base into the current
-process before running the corresponding test. This can be useful as a shortcut
+For convenience, there are also `test-revise-*` targets for every [`test-*`
+target](https://github.com/JuliaLang/julia/blob/master/CONTRIBUTING.md#running-specific-tests) that use Revise to load any modifications to Base into the current
+system image before running the corresponding test. This can be useful as a shortcut
 on the command line (since tests aren't always designed to be run outside the
 runtest harness).