Add SignalR to common repository list (#2205)

Author: NtFreX

CONTRIBUTING.md

@@ -18,6 +18,7 @@ For non-security related bugs please log a new issue in the appropriate GitHub r
 * [Razor](https://github.com/aspnet/Razor)
 * [Templates](https://github.com/aspnet/Templates)
 * [Tooling](https://github.com/aspnet/Tooling)
+* [SignalR](https://github.com/aspnet/SignalR)
 
 Or browse the full list of repos in the [aspnet](https://github.com/aspnet/) organization.
 
@@ -88,4 +89,4 @@ Addresses #bugnumber (in this specific format)
 
 **Feedback**
 
-Your pull request will now go through extensive checks by the subject matter experts on our team. Please be patient; we have hundreds of pull requests across all of our repositories. Update your pull request according to feedback until it is approved by one of the ASP.NET team members. After that, one of our team members will add the pull request to **dev**.
+Your pull request will now go through extensive checks by the subject matter experts on our team. Please be patient; we have hundreds of pull requests across all of our repositories. Update your pull request according to feedback until it is approved by one of the ASP.NET team members. After that, one of our team members will add the pull request to **dev**.