Add a "how to cite" section (#401)

* new how-to-cite section

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix formatting

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: brian-rose

CITATION.cff

@@ -1,5 +1,5 @@
 cff-version: 1.2.0
-message: 'If you use this software, please cite it as below.'
+message: 'If you use this resource, please cite it as below.'
 authors:
   - family-names: Rose
     given-names: Brian E. J.
@@ -46,3 +46,4 @@ authors:
 title: 'Pythia Foundations'
 version: v2023.05.01
 date-released: 2023-05-01
+doi: 10.5281/zenodo.7884572

_toc.yml

@@ -4,6 +4,7 @@ parts:
   - caption: Preamble
     chapters:
       - file: preamble/how-to-use
+      - file: preamble/how-to-cite
   - caption: Foundational skills
     chapters:
       - file: foundations/overview

landing-page.md

@@ -7,3 +7,5 @@
 This collection covers the foundational skills everyone needs to get started with scientific computing in the open-source Python ecosystem.
 
 <img src="images/logos/ProjectPythia_Logo_Final-01-Blue.svg" alt="Project Pythia logo" height="80px"> _Brought to you by [Project Pythia](https://projectpythia.org), the education working group for [Pangeo](https://pangeo.io)_ <img src="https://raw.githubusercontent.com/pangeo-data/pangeo/master/docs/_static/small_e_logo_cropped.png" alt="Pangeo logo" height="80px">
+
+[![DOI](https://zenodo.org/badge/338145160.svg)](https://zenodo.org/badge/latestdoi/338145160)

preamble/how-to-cite.md

@@ -0,0 +1,10 @@
+# How to Cite This Book
+
+The material in Pythia Foundations is licensed for free and open consumption and reuse. All code is served under [Apache 2.0](https://www.apache.org/licenses/LICENSE-2.0), while all non-code content is licensed under [Creative Commons BY 4.0 (CC BY 4.0)](https://creativecommons.org/licenses/by/4.0/). Effectively, this means you are free to share and adapt this material so long as you give appropriate credit to the Project Pythia community.
+
+The source code for the book is [released on GitHub](https://github.com/ProjectPythia/pythia-foundations) and archived on Zenodo. This DOI will always resolve to the latest version of the book source:
+<https://doi.org/10.5281/zenodo.7884571>
+
+If material in Pythia Foundations is useful in published work, you can cite a specific version of the book as:
+
+> Rose, B. E. J., Kent, J., Tyle, K., Clyne, J., Banihirwe, A., Camron, D., May, R., Grover, M., Ford, R. R., Paul, K., Morley, J., Eroglu, O., Kailyn, L., & Zacharias, A. (2023). Pythia Foundations (Version v2023.05.01) [https://doi.org/10.5281/zenodo.7884572](https://doi.org/10.5281/zenodo.7884572)