readme: describe alpha sdk build process

Co-authored-by: Ethan Pullen <[email protected]>
Co-authored-by: Matthew James Briggs <[email protected]>

local/README.md

@@ -1,3 +1,55 @@
+# Building The Alpha SDK
+
+## Required tools
+* git
+* cargo
+* docker
+
+## Clone Bottlerocket
+
+We will start by cloning Bottlerocket so it can be used to create the alpha variant.
+
+```bash
+git clone https://github.com/bottlerocket-os/bottlerocket.git
+```
+
+## Clone Twoliter
+
+Next we will clone the twoliter project.
+
+```bash
+git clone https://github.com/bottlerocket-os/twoliter.git
+```
+
+## Build the alpha sdk
+
+The alpha sdk script will build bottlerocket from the main repo, so we need to provide it's path.
+Add the path to the command below.
+
+```bash
+BOTTLEROCKET_PROJECT_DIR=
+```
+
+Next we need to configure the image that is created by twoliter.
+```bash
+# The ecr registry the alpha sdk should be pushed to
+ALPHA_SDK_REGISTRY=
+# The version for this alpha sdk
+ALPHA_SDK_VERSION=
+```
+
+To build the sdk we need to call the `alpha-sdk.sh` script.
+
+```bash
+# From within the twoliter project
+cd local
+./alpha-sdk.sh \
+    --bottlerocket-dir ${BOTTLEROCKET_PROJECT_DIR} \
+    --alpha-registry ${ALPHA_SDK_REGISTRY} \
+    --alpha-version ${ALPHA_SDK_VERSION}
+cd ..
+```
+
 # The Local Directory
 
 This directory is for scripts involved with building and testing Twoliter.