backmatter: Add critical information

1 files changed, 42 insertions, 0 deletions

diff --git a/spec/back-matter.md b/spec/back-matter.md
index 7eac512..25ded14 100644
--- a/spec/back-matter.md
+++ b/spec/back-matter.md
@@ -6,3 +6,45 @@ maintained by the [Tor Project](https://www.torproject.org/).
 
 Only the Tor Specifications themselves are approved.
 The [Proposals](../proposals/) are, by their nature, drafts.
+
+## Source code
+
+The Specifications and Proposals are maintained by the Tor Project
+in a
+[gitlab repository](https://gitlab.torproject.org/tpo/core/torspec/).
+
+Corrections and clarifications are welcome.
+To propose a change to the Tor protocol, use the
+[Proposals process](proposals/001-process.txt)
+
+## Building
+
+The documents are in Markdown and formatted with
+[mdbook](https://rust-lang.github.io/mdBook/).
+To build the formatted HTML:
+
+```text,ignore
+cargo install mdbook
+git clone https://gitlab.torproject.org/tpo/core/torspec/
+cd torspec
+bin/build_html
+```
+
+The output is then in `html/`.
+
+## Source code structure, and output webtree
+
+There are two mdbook books here:
+
+ * **The Tor Specifications**: source code in `specs/`,
+   formatted output in `html/`.
+
+ * **Proposals**: source code in `proposals/`,
+   formatted output in `html/proposals/`.
+
+Each book's source files are listed,
+and the chapter defined,
+in its `SUMMARY.md`.
+The format is pretty restrictive;
+see the
+[mdbook documentation](https://rust-lang.github.io/mdBook/format/summary.html).