Reformat a table in contributing.md (#6)

Signed-off-by: Jonathan Schwender <[email protected]>

src/contributing.md

@@ -46,13 +46,13 @@ When you push to a pull request, GitHub automatically checks that your changes h
 To run unit tests or Web Platform Tests against a pull request, add one or more of the labels below to your pull request.
 If you do not have permission to add labels to your pull request, add a comment on your bug requesting that they be added.
 
-| Label | Runs unit tests on | Runs web tests on |
-|---|---|---|
-| `T-full` | All platforms | Linux |
-| `T-linux-wpt-2013` | Linux | Linux (only legacy layout) |
-| `T-linux-wpt-2020` | Linux | Linux (skip legacy layout) |
-| `T-macos` | macOS | (none) |
-| `T-windows` | Windows | (none) |
+| Label              | Runs unit tests on | Runs web tests on          |
+|--------------------|--------------------|----------------------------|
+| `T-full`           | All platforms      | Linux                      |
+| `T-linux-wpt-2013` | Linux              | Linux (only legacy layout) |
+| `T-linux-wpt-2020` | Linux              | Linux (skip legacy layout) |
+| `T-macos`          | macOS              | (none)                     |
+| `T-windows`        | Windows            | (none)                     |
 
 ## AI contributions