Use proper Email links

Without this GitLab thinks these are references to the gitlab.com group.

README.md

@@ -9,9 +9,9 @@ tracker.
 ## Contact Details
-| Name            | Role   | Email                   | GitLab.com     | Slack          |
-|:----------------|:-------|:------------------------|:---------------|:---------------|
-| Yorick Peterse  | Mentor | yorick@gitlab.com       | @yorickpeterse | @yorickpeterse |
-| Heather McNamee | Coach  | heather@gitlab.com      | @nearlythere   | @heather       |
-| Grzegorz Bizon  | Coach  | grzegorz@gitlab.com     | @grzesiek      | @grzegorz      |
-| Tomasz Maczukin | Coach  | tomasz@gitlab.com       | @tmaczukin     | @tmaczukin     |
+| Name            | Role   | Email                     | GitLab.com     | Slack          |
+|:----------------|:-------|:--------------------------|:---------------|:---------------|
+| Yorick Peterse  | Mentor | <yorick@gitlab.com>       | @yorickpeterse | @yorickpeterse |
+| Heather McNamee | Coach  | <heather@gitlab.com>      | @nearlythere   | @heather       |
+| Grzegorz Bizon  | Coach  | <grzegorz@gitlab.com>     | @grzesiek      | @grzegorz      |
+| Tomasz Maczukin | Coach  | <tomasz@gitlab.com>       | @tmaczukin     | @tmaczukin     |