Add top level manifest to build the Zephyr integration project

To verify, use the same steps as in the README file but substitite
the first steps (the checkout) with:

1. Clone the empty manifest repo
2. Cherry-pick this change
3. Run repo init from a local manifest via
   `$ repo init -u file://$(pwd) -b main -m manifest.xml --depth 1`

Change-Id: I667176389c78b00b621e068b51be7216b56ccb42
Signed-off-by: Yuval Peress <peress@google.com>
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/zephyr-manifest/+/130390
Reviewed-by: Rob Mohr <mohrr@google.com>

README.md

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..691a6b7
--- /dev/null
+++ b/README.md
@@ -0,0 +1,17 @@
+# Getting started using Repo
+
+This manifest is currently pinned to Zephyr v3.3
+
+```
+$ mkdir zephyr-pigweed-integration
+$ cd zephyr-pigweed-integration
+$ repo init -u sso://pigweed/pigweed/zephyr-manifest -b main -m manifest.xml
+$ repo sync
+$ cd workspace
+$ . pigweed/bootstrap.sh
+$ pip install -r zephyr/scripts/requirements.txt
+$ ./zephyr/scripts/twister -v -c -i -T samples/ \
+  -x=ZEPHYR_MODULES="$(pwd)/nanopb;$(pwd)/pigweed" \
+  -x=ZEPHYR_BASE=$(pwd)/zephyr
+```
+

manifest.xml

diff --git a/manifest.xml b/manifest.xml
new file mode 100644
index 0000000..27cced7
--- /dev/null
+++ b/manifest.xml
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<manifest>
+	<remote name="zephyrproject-rtos"
+		fetch="https://github.com/zephyrproject-rtos"
+		revision="v3.3-branch"/>
+	<remote name="pigweed"
+		fetch="https://pigweed.googlesource.com/pigweed"
+		revision="main"/>
+
+	<project name="zephyr"
+		remote="zephyrproject-rtos"
+		path="zephyr"/>
+	<project name="nanopb"
+		remote="zephyrproject-rtos"
+		revision="zephyr"
+		path="nanopb"/>
+	<project name="pigweed"
+		remote="pigweed"
+		path="workspace/pigweed"/>
+	<project name="zephyr-integration"
+		remote="pigweed"
+		path="."/>
+</manifest>