CONTRIBUTING.md: Some minor clean-ups

CONTRIBUTING.md

@@ -70,10 +70,9 @@
 
 ## Commit policy
 
-* Commits must be sufficiently tested before being merged, both the master and staging branches.
-* Hydra builds for master and stagingshould not be used as testing platform, it's a build farm for changes that have been already tested.
+* Commits must be sufficiently tested before being merged, both for the master and staging branches.
+* Hydra builds for master and staging should not be used as testing platform, it's a build farm for changes that have been already tested.
 * Master should only see non-breaking commits that do not cause mass rebuilds.
-* Staging should only see non-breaking mass-rebuild commits. That means it's not to be used for testing, changes must have been well tested already. [Read policy here](http://comments.gmane.org/gmane.linux.distributions.nixos/13447).
+* Staging should only see non-breaking mass-rebuild commits. That means it's not to be used for testing, and changes must have been well tested already. [Read policy here](http://comments.gmane.org/gmane.linux.distributions.nixos/13447).
 * If staging is already in a broken state, please refrain from adding extra new breakages. Stabilize it for a few days, merge into master, then resume development on staging. [Keep an eye on the staging evaluations here](http://hydra.nixos.org/jobset/nixpkgs/staging#tabs-evaluations).
-* When changing the bootloader installation process, extra care must be taken. Grub installations cannot be rolled back, hence changes may break people installation forever. For any non-trivial change to the bootloader please file a PR asking for review, especially from @edolstra.
-
+* When changing the bootloader installation process, extra care must be taken. Grub installations cannot be rolled back, hence changes may break people's installations forever. For any non-trivial change to the bootloader please file a PR asking for review, especially from @edolstra.