feat: documents and session tokens

spec/README.md

@@ -1,8 +1,22 @@
 # The scienting specifications
 
-These chapters are the normative text of `spec` 0.1.
+This is the specification of the scienting formats: exactly what each file holds and how every value in it is computed.
+For what the formats are for, start with the [guides](../docs/README.md); this text assumes you know why and tells you how.
 Schemas, SQL, the JSON-LD context, the registries, the vectors and the fixtures are normative too, and the chapters say which.
-Where a chapter and a vector disagree, the disagreement is a bug in this repository; report it.
+Where a chapter and a vector disagree, the disagreement is a bug; please report it.
+
+## Reading paths
+
+| If you are writing | Read |
+| --- | --- |
+| Anything at all | 0, 1, 3, 4 and 5: conventions, nodes, identity and the content values. |
+| A reader of packages | Then 2, 6, 7 and 12: the model, anchors, geometry and the package. |
+| A converter | Then 9, 10 and 11: figures and tables, references, and corrections with the gate. |
+| A store or a server | Then 8, 13 and 14: receipts, the database form, and rights. |
+| A tool for annotation, teaching or data | Then 15 to 21. |
+| A validator | Chapter 22, with [registry/rules.json](../registry/rules.json). |
+
+## Chapters
 
 | Chapter | Subject |
 | --- | --- |