Adding readme file the retrieve

dependency/README.md

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+# Dependency
+
+Pre-compiled distributions of Python are provided for the Paketo stacks (i.e.
+`io.buildpacks.stack.jammy` and `io.buildpacks.stacks.bionic`).
+
+Source distributions of Python are provided for all other linux stacks.
+
+This directory contains scripts and GitHub Actions to facilitate the following:
+* Identifying when there is a new version of Python available
+* Compiling Python against all supported stacks
+* Packing the Python source for use in all other stacks (i.e. where we do not
+provide pre-compiled binaries of python)
+
+## Running locally
+
+Running the steps locally can be useful for iterating on the compilation process
+(e.g. changing compilation options) as well as debugging.
+
+### Retrieval
+
+Retrieve latest versions with:
+
+```
+cd ./retrieval
+
+go run main.go \
+  --buildpack-toml-path ../../buildpack.toml \
+  --output /path/to/retrieved.json
+```
+
+See [retrieval/README.md](retrieval/README.md) for more details.
+
+### Compilation
+
+To compile on Ubuntu 22.04 (Jammy):
+
+```
+docker build \
+  --tag cpython-compilation-jammy \
+  --file ./actions/compile/jammy.Dockerfile \
+  ./actions/compile
+
+output_dir=$(mktemp -d)
+
+docker run \
+  --volume $output_dir:/tmp/compilation \
+  cpython-compilation-jammy \
+    --outputDir /tmp/compilation \
+    --target jammy \
+    --version 3.10.7
+```
+
+See [actions/compile/README.md](actions/compile/README.md) for more details.