docs: add documentation for declaring module dependencies using #Requires statements

Co-authored-by: MariusStorhaug <17722253+MariusStorhaug@users.noreply.github.com>

Author: Copilot

README.md

@@ -919,7 +919,7 @@ How the module is built.
 │   ├── formats/                            # Formatting metadata registered during build
 │   │   ├── CultureInfo.Format.ps1xml       # Example format included in manifest
 │   │   └── Mygciview.Format.ps1xml         # Additional format loaded at import
-│   ├── functions/                          # Function scripts exported by the module
+│   ├── functions/                          # Function scripts exported by the module; #Requires -Modules statements here are compiled into RequiredModules
 │   │   ├── private/                        # Helper functions scoped to the module
 │   │   │   ├── Get-InternalPSModule.ps1    # Sample internal helper
 │   │   │   └── Set-InternalPSModule.ps1    # Sample internal helper
@@ -949,10 +949,58 @@ How the module is built.
 │   │       └── SolarSystems.ps1            # Example variable surfaced in generated docs
 │   ├── finally.ps1                         # Cleanup script appended to the root module
 │   ├── header.ps1                          # Optional header injected at the top of the module
-│   ├── manifest.psd1 (optional)            # Source manifest reused when present
+│   ├── manifest.psd1 (optional)            # Source manifest reused when present; RequiredModules is not propagated — use #Requires -Modules in function files instead (see "Declaring module dependencies" below)
 │   └── README.md                           # Module-level docs ingested by Document-PSModule
 ```
 
+### Declaring module dependencies
+
+Module dependencies are declared using [`#Requires -Modules`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_requires)
+statements at the top of individual PowerShell function files under `src/functions/public/` and `src/functions/private/`.
+The build system ([Build-PSModule](https://github.com/PSModule/Build-PSModule)) collects all `#Requires -Modules`
+declarations across every source file, de-duplicates them, and writes the merged result into the `RequiredModules` field
+of the compiled module manifest.
+
+> [!IMPORTANT]
+> Adding `RequiredModules` to `src/manifest.psd1` is **not** supported for this purpose. Those entries are silently
+> ignored by the build — they will not appear in the built manifest. Use `#Requires -Modules` in function files instead.
+
+#### Supported syntax variants
+
+```powershell
+# Bare module name — any version is acceptable
+#Requires -Modules Microsoft.Graph.Authentication
+
+# Minimum version constraint
+#Requires -Modules @{ ModuleName = 'Microsoft.Graph.Authentication'; ModuleVersion = '2.28.0' }
+
+# Exact version constraint
+#Requires -Modules @{ ModuleName = 'PSSemVer'; RequiredVersion = '1.1.4' }
+```
+
+#### Example
+
+A function that calls into `Microsoft.Graph.Authentication` declares its dependency at the top of the file:
+
+```powershell
+#Requires -Modules @{ ModuleName = 'Microsoft.Graph.Authentication'; ModuleVersion = '2.28.0' }
+
+function Get-GraphToken {
+    ...
+}
+```
+
+When the module is built, the compiled manifest automatically includes:
+
+```powershell
+RequiredModules = @(
+    @{ ModuleName = 'Microsoft.Graph.Authentication'; ModuleVersion = '2.28.0' }
+)
+```
+
+This co-location approach keeps dependency declarations next to the functions that need them, making it immediately
+clear which commands drive each external dependency.
+
 ## Principles and practices
 
 The contribution and release process is based on the idea that a PR is a release, and we only maintain a single linear ancestry of versions, not going