Add description of Go internal modules (#12336)

* Add description of Go internal modules

* Apply suggestions from code review

Co-authored-by: Wojciech Sołtys <74361703+Sawthis@users.noreply.github.com>

* Update cmd/image-builder/image-builder.md

Co-authored-by: Iwona Langer <iwona.langer@sap.com>

---------

Co-authored-by: Wojciech Sołtys <74361703+Sawthis@users.noreply.github.com>
Co-authored-by: Iwona Langer <iwona.langer@sap.com>

cmd/image-builder/image-builder.md

@@ -165,4 +165,11 @@ The flag value is base64-encoded to avoid issues with special characters in the
 
 The `--env-file` specifies the path to the file with environment variables to be loaded in the build.
 All variables and their values are loaded into the environment before the build starts.
-The file must be in the format of `KEY=VALUE` pairs, separated by newlines.
+The file must be in the format of `KEY=VALUE` pairs, separated by newlines.
+
+## Access Golang SAP Internal Modules
+
+You can use Image Builder to build images that require access to Go SAP internal modules. To use this feature, set the `--use-go-internal-sap-modules=true` flag.
+The feature is only available for the ADO backend. 
+
+This feature utilizes the `go` vendor mechanism by downloading all the dependencies into the `vendor` directory. There is no option to pass custom credentials for fetching the dependencies; the tool handles it internally.