Add beginner onboarding README and teaching comments

README.md

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+# Hello, OpenLambda! 👋
+
+This is the simplest possible [OpenLambda](https://github.com/open-lambda/open-lambda)
+function — the "hello world" of serverless. If you've never written a serverless
+function before, start here.
+
+## What is a lambda?
+
+A lambda is just a small function that runs on demand. You don't manage a server,
+a `main()`, or a web framework — you write one function, and OpenLambda runs it
+whenever someone calls it.
+
+The entire program is [`f.py`](f.py):
+
+```python
+def f(event):
+    return 'hello'
+```
+
+The contract is tiny:
+
+- The function **must be named `f`**.
+- It takes **one argument, `event`** — the data sent in the request.
+- Whatever you **`return`** becomes the response (encoded as JSON).
+
+## Prerequisites
+
+You need a running OpenLambda worker. OpenLambda runs on **Linux (Ubuntu 24.04 LTS)**,
+needs root privileges, and cgroups v2 — so on macOS/Windows use a Linux VM or container.
+
+Follow the [Getting Started guide](https://github.com/open-lambda/open-lambda/blob/main/docs/worker/getting-started.md)
+to build and start a worker. The short version:
+
+```bash
+make ol imgs/ol-min     # build (Python-only)
+./ol worker init -i ol-min
+./ol worker up          # starts the worker on localhost:5000
+```
+
+## Run this function
+
+With a worker running, install this function straight from GitHub:
+
+```bash
+./ol admin install https://github.com/open-lambda/hello-lambda-example.git
+```
+
+The function name is taken from the repo name, so invoke it like this:
+
+```bash
+curl -X POST localhost:5000/run/hello-lambda-example -d ''
+```
+
+You should get back:
+
+```
+"hello"
+```
+
+🎉 You just ran your first serverless function.
+
+## Now change it
+
+Open [`f.py`](f.py) and make it greet you by name. The request body is passed in
+as `event`, so you can read from it:
+
+```python
+def f(event):
+    name = event.get('name', 'world')
+    return f'hello, {name}!'
+```
+
+Reinstall and call it again, this time sending some JSON:
+
+```bash
+./ol admin install https://github.com/open-lambda/hello-lambda-example.git
+curl -X POST localhost:5000/run/hello-lambda-example -d '{"name": "Ada"}'
+```
+
+→ `"hello, Ada!"`
+
+That's the whole loop: **edit `f.py` → install → curl**.
+
+## What's next?
+
+- Need a Python package? Add a `requirements.txt` next to `f.py` and OpenLambda
+  installs it for you.
+- Browse the [`examples/`](https://github.com/open-lambda/open-lambda/tree/main/examples)
+  directory in the main repo — numpy, pandas, Flask, and more.
+- Read the [worker docs](https://github.com/open-lambda/open-lambda/tree/main/docs/worker)
+  to learn how OpenLambda runs your code fast.
+
+Welcome to serverless. 🚀

f.py

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+# This is an OpenLambda function — a tiny serverless program.
+#
+# The whole contract is just this:
+#   * Define a function named `f`.
+#   * It takes ONE argument, `event` — the data sent in the request.
+#   * Whatever you `return` becomes the response (sent back as JSON).
+#
+# That's it. No servers to manage, no main(), no framework.
 def f(event):
     return 'hello'