doc: book skeloton (#7675)

#7670

book/src/README.md

@@ -1,6 +1,30 @@
 # Introduction
 
-Welcome to the nearcore development guide!
+Welcome to nearcore development guide!
 
-This will soon become a place for all docs related to implementation of nearcore itself!
-At thi moment, this is under construction, stay tuned :o)
+The target audience of this guide are developers of nearcore itself. If you are
+a user of NEAR (either a contract developer, or validator running a node),
+please refer to the user docs at <https://docs.near.org>.
+
+This guide is build with [mdBook](https://rust-lang.github.io/mdBook/index.html)
+from sources in the [nearcore repository](https://github.com/near/nearcore/).
+You can edit it by pressing the "edit" icon in the top right corner, so feel
+free to correct all the typos and such. The guide is hosted at
+<https://near.github.io/nearcore/>.
+
+The guide is organized as a collection of loosely coupled chapters -- you don't
+need to read it in order, feel free to peruse the TOC and focus on interesting
+bits. The chapters are classified into three parts:
+
+* [**Architecture**](./architecture/index.html) talks about how the code works.
+  So, for example, if you are interested in how a transaction flows through the
+  system, look there!
+* [**Practices**](./practices/index.html) describe, broadly, how we write the code.
+  For example, if you want to learn about code style, issue tracking, or
+  debugging performance problems, this is a chapter for you.
+* Finally, the [**Misc**](./misc/index.html) part holds various assorted bit and
+  pieces. We are trying to bias ourself towards writing more docs, so, if you
+  want to document something and it doesn't cleanly map to any category, just
+  put it in misc!
+
+If you are unsure, start with the next chapter, [Architecture Overview](./architecture/index.html)

book/src/SUMMARY.md

@@ -1,3 +1,15 @@
 # Summary
 
 [Introduction](README.md)
+
+# Architecture
+
+- [Overview](./architecture/README.md)
+
+# Practices
+
+- [Overview](./practices/README.md)
+
+# Misc
+
+- [Misc](./misc/README.md)

book/src/architecture/README.md

@@ -0,0 +1,3 @@
+# Overview
+
+This chapter describes how `nearcore` works.

book/src/misc/README.md

@@ -0,0 +1,4 @@
+# Overview
+
+This chapter holds various assorted bits of docs. If you want to document
+something, but don't know where to put it, put it here!

book/src/practices/README.md

@@ -0,0 +1,4 @@
+# Overview
+
+This chapter describes various development processes and best practices employed
+at nearcore.