add what next page to scheme tutorial

docs/docs/scheme-intro/next-step.md

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+# What Next
+
+If you want to learn more about Scheme, these are the resources I recommend:
+
+## Scheme
+
+* [Sketchy Scheme](https://www.t3x.org/sketchy/) by [Nils M Holm](https://www.t3x.org/)
+
+![Sketchy Scheme Book Cover](./img/sketchy-scheme.png)
+
+There is free version in Archive.org called [Sketchy Lisp](https://archive.org/details/sketchy-lisp) but I recommend latest version.
+
+* [Structure and Interpretation of Computer Programs](https://web.mit.edu/6.001/6.037/sicp.pdf)
+
+A classic, one of the authors of the book is the author of Scheme language.
+
+![SICP Cover](./img/SICP-cover.jpg)<br/>
+<small><a href="https://commons.wikimedia.org/wiki/File:SICP_cover.jpg">Harold Abelson and Gerald Jay Sussman with Julie Sussman — MIT Press</a>, <a href="https://creativecommons.org/licenses/by-sa/4.0">CC BY-SA 4.0</a>, Wikimedia Commons</small>
+
+I also recommend video lectures. There are two versions. I recommend orignal by Abelson and Sussman from 1986.
+
+[![SICP MIT Lectures](./img/SICP-lectures.jpg)](https://www.youtube.com/playlist?list=PLB63C06FAF154F047)
+
+This is [offical website of the lectures](https://groups.csail.mit.edu/mac/classes/6.001/abelson-sussman-lectures/).
+
+They are not very good quality, but they are great and you should have no problems in seeing the code on the blackboard.
+
+There are also more recent lectures from 2010 at Berkley by [Brian Harvey](https://people.eecs.berkeley.edu/~bh/).
+Only a little bit better quality.
+
+[![UC Berkeley CS 61A The Structure and Interpretation of Computer Programs, Spring 2010](./img/SCIP-lectures-berkley.jpg)](https://www.youtube.com/playlist?list=PLhMnuBfGeCDNgVzLPxF9o5UNKG1b-LFY9)
+
+## Lisp Macros
+
+If you want to learn more about lisp macros there are two great books:
+
+* [On Lisp](https://www.paulgraham.com/onlisp.html) by [Paul Graham](https://www.paulgraham.com)
+
+  The book is out of print and you can download it for free. But if you prefer printed books you can get it printed on Lulu Express.
+
+  Here is article that explain how to do this:
+
+* [Piecing Together a Printed Copy of "On Lisp"](https://www.lurklurk.org/onlisp/onlisp.html)
+
+  You can also read this [discussion on Reddit](https://www.reddit.com/r/lisp/comments/l71amc/on_lisp_paperback_replica/).
+
+* Antoher great book about advanced lisp macros is [Let over Lambda](https://letoverlambda.com/) by [Doug Hoyte](https://hoytech.com/).