[embedder] Local Fuchsia requires TAP.

Fixed: 115216
Change-Id: Iecdfd8b685653fad8dce30c235881b0a35d91b40
Reviewed-on: https://fuchsia-review.googlesource.com/c/flutter-embedder/+/759391
Reviewed-by: Naud Ghebre <naudzghebre@google.com>
diff --git a/docs/testing_fuchsia_sdk_changes.md b/docs/testing_fuchsia_sdk_changes.md
index 94950a9..474b618 100644
--- a/docs/testing_fuchsia_sdk_changes.md
+++ b/docs/testing_fuchsia_sdk_changes.md
@@ -19,10 +19,17 @@
    fx set workstation_eng.qemu-x64
    ```
 
-3. Set `$LOCAL_FUCHSIA_PLATFORM_BUILD` to your out directory for your Fuchsia build.
+3. Configure IPv6 networking for Fuchsia ([reference](https://fuchsia.dev/fuchsia-src/get-started/set_up_femu#configure-ipv6-network)):
+
+   ```sh
+   sudo ip tuntap add dev qemu mode tap user $USER
+   sudo ip link set qemu up
+   ```
+
+4. Set `$LOCAL_FUCHSIA_PLATFORM_BUILD` to your out directory for your Fuchsia build.
    For example:
 
-   ```
+   ```sh
    export LOCAL_FUCHSIA_PLATFORM_BUILD=$FUCHSIA_DIR/out/default
    ```
 
@@ -30,12 +37,12 @@
 
 1. Make your platform changes to the Fuchsia checkout that `$LOCAL_FUCHSIA_PLATFORM_BUILD` points to.
 
-2. Build Fuchsia and start the emulator.
+2. Build Fuchsia and start the emulator in TAP mode.
 
    ```sh
    cd $LOCAL_FUCHSIA_PLATFORM_BUILD
    fx build
-   fx ffx emu start
+   fx ffx emu start --net tap
    ```
 
 3. Run an example using `--with-fuchsia` to build the embedder against