Document NuGet as supported by DS

Add NuGet to the list of package managers
supported by Dependency Scanning.

doc/user/application_security/dependency_scanning/index.md

@@ -60,6 +60,7 @@ The following languages and dependency managers are supported:
 
 | Language (package managers)  | Supported files | Scan tool(s) |
 |----------------------------- | --------------- | ------------ |
+| C# .NET ([NuGet](https://www.nuget.org/) 4.9+) | [`packages.lock.json`](https://docs.microsoft.com/en-us/nuget/consume-packages/package-references-in-project-files#enabling-lock-file) | [Gemnasium](https://gitlab.com/gitlab-org/security-products/gemnasium) |
 | Java ([Gradle](https://gradle.org/), [Maven](https://maven.apache.org/)) | `build.gradle`, `build.gradle.kts`, `pom.xml` | [Gemnasium](https://gitlab.com/gitlab-org/security-products/gemnasium) |
 | JavaScript ([npm](https://www.npmjs.com/), [yarn](https://classic.yarnpkg.com/en/)) | `package-lock.json`, `npm-shrinkwrap.json`, `yarn.lock` | [Gemnasium](https://gitlab.com/gitlab-org/security-products/gemnasium), [Retire.js](https://retirejs.github.io/retire.js/) |
 | Go ([Golang](https://golang.org/)) | `go.sum` | [Gemnasium](https://gitlab.com/gitlab-org/security-products/gemnasium) |