doc: update the mdbook instructions (#1521)

doc/dev/mdbook.md

@@ -1,3 +1,12 @@
+# Documentation
+
+The Lean `doc` folder contains the [Lean Manual](https://leanprover.github.io/lean4/doc/) and is
+authored in a combination of markdown (*.md) files and literate Lean files.  The .lean files are
+preprocessed using a tool called [LeanInk](https://github.com/leanprover/leanink) and
+[Alectryon](https://github.com/Kha/alectryon) which produces a generated markdown file.  We then run
+`mdbook` on the result to generate the html pages.
+
+
 ## Settings
 
 We are using the following settings while editing the markdown docs.
@@ -14,30 +23,84 @@ We are using the following settings while editing the markdown docs.
 
 ## Build
 
-This manual is generated by
-[mdBook](https://github.com/rust-lang/mdBook). We are currently using
-a [fork](https://github.com/leanprover/mdBook) of it for the following
-additional features:
+### Using Nix
+
+Building the manual using Nix (which is what the CI does) is as easy as
+```bash
+$ nix build --update-input lean ./doc
+```
+You can also open a shell with `mdbook` for running the commands mentioned below with
+`nix develop ./doc#book`. Otherwise, read on.
+
+### Manually
+
+To build and test the book you have to preprocess the .lean files with Alectryon then use our own
+fork of the Rust tool named [mdbook](https://github.com/leanprover/mdbook). We have our own fork of
+mdBook with the following additional features:
 
 * Add support for hiding lines in other languages
   [#1339](https://github.com/rust-lang/mdBook/pull/1339)
-* Replace calling `rustdoc --test` from `mdbook test` with `./test`
+* Make `mdbook test` call the `lean` compiler to test the snippets.
+* Ability to test a single chapter at a time which is handy when you
+are working on that chapter.  See the `--chapter` option.
 
-To build this manual, first install the fork via
-```bash
-cargo install --git https://github.com/leanprover/mdBook mdbook
-```
-Then use e.g. [`mdbook watch`](https://rust-lang.github.io/mdBook/cli/watch.html) in the `doc/` folder:
+So you need to setup these tools before you can run `mdBook`.
 
-```bash
-cd doc
-mdbook watch --open  # opens the output in `out/` in your default browser
-```
+1. install [Rust](https://www.rust-lang.org/tools/install)
+which provides you with the `cargo` tool for building rust packages.
+Then run the following:
+    ```bash
+    cargo install --git https://github.com/leanprover/mdBook mdbook
+    ```
 
-Run `mdbook test` to test all `lean` code blocks.
+1. Clone https://github.com/leanprover/LeanInk.git and run `lake build` then copy the resulting
+executable to your `$HOME/.elan/bin` folder or `%USERPROFILE%\.elan\bin` so Alectryon can find it
+there.
 
-Using the [Nix setup](make/nix.md), you can instead open a shell with
-the mdBook fork downloaded from our binary cache:
-```bash
-nix develop .#doc
-```
+1. Create a Python 3.10 environment.
+
+1. Install the following packages:
+    ```
+    python3 -m pip install git+https://github.com/Kha/alectryon.git@typeid
+    ```
+
+1. Now you are ready to process the *.lean files using Alectryon as follows:
+
+    ```
+    cd lean4/doc
+    alectryon --frontend lean4+markup examples\palindromes.lean --backend webpage -o palindromes.lean.md
+    ```
+
+And repeat this for the other .lean files you care about or write a script to process them all.
+
+1. Now you can build the book using:
+    ```
+    cd lean4/doc
+    mdbook build
+    ```
+
+This will put the HTML in a `out` folder so you can load `out/index.html` in your web browser and
+it should look like https://leanprover.github.io/lean4/doc/.
+
+1. It is also handy to use e.g. [`mdbook watch`](https://rust-lang.github.io/mdBook/cli/watch.html)
+   in the `doc/` folder so that it keeps the html up to date while you are editing.
+
+    ```bash
+    mdbook watch --open  # opens the output in `out/` in your default browser
+    ```
+
+## Testing Lean Snippets
+
+You can run the following in the `doc/` folder to test all the lean code snippets.
+
+    ```bash
+    mdbook test
+    ```
+
+and you can use the `--chapter` option to test a specific chapter that you are working on:
+
+    ```bash
+    mdbook test --chapter Array
+    ```
+
+Use chapter name `?` to get a list of all the chapter names.