Document specifying lists in MsBuild properties (#30117)

src/csharp/BUILD-INTEGRATION.md

@@ -343,7 +343,7 @@ The following metadata are recognized on the `<Protobuf>` items.
 | Name           | Default   | Value                | Synopsis                         |
 |----------------|-----------|----------------------|----------------------------------|
 | Access         | `public`  | `public`, `internal`               | Generated class access           |
-| AdditionalProtocArguments | | arbitrary cmdline arguments | Extra command line flags passed to `protoc` command |
+| AdditionalProtocArguments | | arbitrary cmdline arguments | Extra command line flags passed to `protoc` command. To specify multiple arguments use semi-colons (;) to separate them. See example below |
 | ProtoCompile   | `true`    | `true`, `false`                    | Pass files to protoc?            |
 | ProtoRoot      | See notes | A directory                        | Common root for set of files     |
 | CompileOutputs | `true`    | `true`, `false`                    | C#-compile generated files?      |
@@ -389,6 +389,23 @@ and "GrpcServices" metadata, but it might be useful in situations where you want
 to explicitly pass some otherwise unsupported (e.g. experimental) options to the
 `grpc_csharp_plugin`.
 
+__Specifying multiple values in properties__
+
+Some properties allow you to specify multiple values in a list. The items in a list need to
+be separated by semi-colons (;). This is the syntax that MsBuild uses for lists.
+
+The properties that can have lists of items are: __OutputOptions__, __AdditionalProtocArguments__, __GrpcOutputOptions__
+
+Example: to specify two additional arguments: ```--plugin=protoc-gen-myplugin=D:\myplugin.exe --myplugin_out=.```
+
+```xml
+  <ItemGroup>
+    <Protobuf Include="proto_root/**/*.proto" ProtoRoot="proto_root"
+              OutputDir="%(RelativeDir)" CompileOutputs="false"
+              AdditionalProtocArguments="--plugin=protoc-gen-myplugin=D:\myplugin.exe;--myplugin_out=." />
+  </ItemGroup>
+```
+
 `grpc_csharp_plugin` command line options
 ---------