docs update with case study (#63)

* docs(manual): add introduction page

* docs(manual): rewrite getting started as guided first run

* docs(manual): rewrite writing specs as a folio tutorial

* docs(manual): document missing spec API in reference

* docs(manual): plain-language rewrite of runs page

* docs: real introductions on index pages and README

* fix(docs): sibling links from directory-style pages need ../

* fix(docs): correct sampling and restart-cost claims to match implementation

* docs: nav lists Introduction and Case study; roadmap points to milestone

* docs(manual): make getting started target the reader's own app, not Folio

* docs(manual): add Folio case study page

* docs: point manual navigation at the case study

* docs(readme): lead with the case study, fix roadmap link

* docs: roadmap links to milestone, sync clear-data default and cross-links

docs/index.md

@@ -4,16 +4,23 @@ title: Sanderling Manual
 
 # Sanderling Manual
 
-Autonomous property-based testing for mobile/web apps. Specs in TypeScript. Core in Go. Drives the app under test through UIAutomation/XCTest on Android/iOS and CDP on web.
+sanderling tests mobile and web apps by exploring them on its own and checking rules you write. You state properties that must always hold ("a new account starts at zero", "the app never throws"). sanderling drives the app for minutes or hours through thousands of taps, swipes, and inputs, and records every step where a property breaks. One TypeScript spec runs against Android, iOS, and web builds of the same app.
 
-Alpha: Scope of v0.1.0 is tracked in [issue #4](https://github.com/priyanshujain/sanderling/issues/4).
+Alpha: the scope of v0.1.0 is tracked in the [v0.1.0 milestone](https://github.com/priyanshujain/sanderling/milestone/1).
 
+## Manual
 
-- [Getting started](./manual/getting-started/)
-- [Writing specs](./manual/writing-specs/)
-- [Runs](./manual/runs/)
-- [Replay](./manual/replay/)
-- [CLI reference](./manual/cli/)
+- [Introduction](./manual/introduction/): what property-based testing is and how sanderling works.
+- [Case study: Folio](./manual/case-study/): sanderling finding a real bug in a mobile app, and how the spec is written.
+- [Getting started](./manual/getting-started/): install the CLI and run it against Folio.
+- [Spec language reference](./manual/spec-language/): every selector, operator, action, and sampler.
+- [Runs](./manual/runs/): what happens during a run and why runs are long.
+- [Replay](./manual/replay/): the trace browser.
+- [CLI reference](./manual/cli/): every command and flag.
+
+## Development
+
+- [Architecture](./development/architecture/) and [design principles](./development/design-principles/) for contributors.
 
 ---