Update readme.source.md

Author: SimonCropp

readme.source.md

@@ -351,6 +351,7 @@ information sources and warn about particular gotchas:
 * [Verify.AngleSharp](https://github.com/VerifyTests/Verify.AngleSharp): Html verification utilities via [AngleSharp](https://github.com/AngleSharp/AngleSharp).
 * [Verify.AspNetCore](https://github.com/VerifyTests/Verify.AspNetCore): Verification of AspNetCore bits.
 * [Verify.Aspose](https://github.com/VerifyTests/Verify.Aspose): Verification of documents (pdf, docx, xlsx, and pptx) via Aspose.
+* [Verify.Assertions](https://github.com/VerifyTests/Verify.Assertions): Extends Verify to allow an assertion callback. This enables using assertion libraries to interrogate during serialization.
 * [Verify.AustralianProtectiveMarkings](https://github.com/pmcau/AustralianProtectiveMarkings): Verification of AustralianProtectiveMarkings.
 * [Verify.Avalonia](https://github.com/VerifyTests/Verify.Avalonia): Verification of [Avalonia UIs](https://avaloniaui.net/).
 * [Verify.Blazor](https://github.com/VerifyTests/Verify.Blazor): Verification of [Blazor Component](https://docs.microsoft.com/en-us/aspnet/core/blazor/#components) Blazor rendering.