docs(relationships): add concrete code examples to README

## Summary

The newly introduced `Azure.ResourceManager.Relationships` package (1.0.0-beta.1, merged in #57520) had a generic boilerplate README with no service-specific code examples. Because `Microsoft.Relationships` introduces novel ARM concepts (`DependencyOf` and `ServiceGroupMember` relationship types), developers need concrete examples to understand how to use the library.

## Changes

### `sdk/relationships/Azure.ResourceManager.Relationships/README.md`

Replaced the generic "Code samples for using the management library for .NET can be found in the following locations" placeholder with four specific, snippet-backed examples covering the primary use cases:

1. **Create a `DependencyOf` relationship** — declares that one Azure resource depends on another
2. **Get a `DependencyOf` relationship** — retrieves an existing relationship
3. **Delete a `DependencyOf` relationship** — removes a dependency relationship
4. **Add a resource to a service group** — creates a `ServiceGroupMember` relationship

### `sdk/relationships/Azure.ResourceManager.Relationships/tests/Samples/RelationshipsSnippets.cs`

New handwritten snippet file containing compilable `[Test]` methods with `#region Snippet:...` / `#endregion` markers. These back the code blocks in the README so that `eng/scripts/Update-Snippets.ps1` can synchronize them and CI can validate they compile.

## Testing

The snippet file uses `[Ignore("Only verifying that the sample builds")]` consistent with the existing auto-generated sample files in the same directory. The code is validated at compile time.

> Generated by [Update Docs](https://github.com/Azure/azure-sdk-for-net/actions/runs/23959312644/agentic_workflow) · [◷](https://github.com/search?q=repo%3AAzure%2Fazure-sdk-for-net+%22gh-aw-workflow-id%3A+update-samples-and-docs%22&type=pullrequests)

---

> [!NOTE]
> This was originally intended as a pull request, but GitHub Actions is not permitted to create or approve pull requests in this repository.
> The changes have been pushed to branch `docs/relationships-readme-examples-a016272957b5622f`.
>
> **[Click here to create the pull request](https://github.com/Azure/azure-sdk-for-net/compare/main...docs/relationships-readme-examples-a016272957b5622f?expand=1&title=docs(relationships)%3A%20add%20concrete%20code%20examples%20to%20README)**

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Show patch preview (223 of 223 lines)

```diff
From 313df1f5cc78c47b21868958988f65d939504819 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
Date: Fri, 3 Apr 2026 19:40:00 +0000
Subject: [PATCH] docs(relationships): add concrete code examples to README

Add snippet-backed code examples to the Azure.ResourceManager.Relationships
README covering the key operations:
- Create a DependencyOf relationship (link two Azure resources)
- Get a DependencyOf relationship
- Delete a DependencyOf relationship
- Add a resource to a service group via ServiceGroupMember relationship

Added RelationshipsSnippets.cs test file with #region Snippet markers so
the examples are backed by compilable code and can be validated by CI.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
.../README.md | 76 ++++++++++++-
.../tests/Samples/RelationshipsSnippets.cs | 104 ++++++++++++++++++
2 files changed, 178 insertions(+), 2 deletions(-)
create mode 100644 sdk/relationships/Azure.ResourceManager.Relationships/tests/Samples/RelationshipsSnippets.cs

diff --git a/sdk/relationships/Azure.ResourceManager.Relationships/README.md b/sdk/relationships/Azure.ResourceManager.Relationships/README.md
index 4915ea2b6..8737d001e 100644
--- a/sdk/relationships/Azure.ResourceManager.Relationships/README.md
+++ b/sdk/relationships/Azure.ResourceManager.Relationships/README.md
@@ -56,8 +56,80 @@ Documentation is available to help you learn how to use this package:

## Examples

-Code samples for using the management library for .NET can be found in the following locations
-- [.NET Management Library Code Samples](https://aka.ms/azuresdk-net-mgmt-samples)
+### Create a DependencyOf relationship
+
+A `DependencyOf` relationship declares that one Azure resource depends on another, enabling dependency mapping and change-impact analysis.
+
+```C# Snippet:Relationships_CreateDependencyOf
+TokenCredential cred = new DefaultAzureCredential();
+ArmClien
... (truncated)
```