feat: update guide.md with instructor notes (#73)

Add a bit of explanation about why the lesson is structured as it is.
This is mostly intended for the instructors who come after, so they
don't misstep like I did.

- resolves #30

guide.md

@@ -1,6 +1,25 @@
 ---
 title: "Instructor Notes"
 ---
-FIXME
+This lesson is a process-oriented tutorial on creating a Python package for Research Software Engineers.
+
+After giving an overview of all the files we're going to touch (on the index page), 
+it follows the process of creating a package:
+- Create a new repository (setup),
+- Create a virtual environment,
+- Add some code and tests,
+- Add important metadata files,
+- Configure the `pyproject.toml` file with detailed metadata,
+- Decide on and implement a versioning scheme,
+- Add automated checks like code linting,
+- Add continuous integration support,
+- Publish the package and make it citeable by adding an additional metadata file.
+
+The lesson is intentionally more challenging than an entry-level how-to guide on packaging.
+At each step when a new concept is introduced, 
+it dives deeper into the detail than a how-to guide would –
+for instance, we only get to code after setting up an environment 
+and initializing the infrastructure needed for reproducible builds.
+
 
 {% include links.md %}