Documentation: install/upgrade/uninstall guides + recipes incl. Zerto

Adds a docs/ folder under the repo root with full operator documentation
aimed at sysadmins (not webhook developers). The Zerto pre/post script
recipe is the canonical "why does this exist" walkthrough; the GitHub
HMAC, AD password reset, and UI-on-desktop recipes round out common
patterns.

Pages:
- README.md (index)
- concepts.md (5-minute "what is a webhook" explainer)
- installation.md (interactive + silent install)
- upgrading.md (single-click upgrade flow + edge cases)
- uninstalling.md (clean removal + wiping ProgramData)
- runas-modes.md (Service / InteractiveUser / SpecificUser decision flow)
- service-account-and-ad.md (gMSA setup, delegated rights)
- network-and-security.md (bind addresses, allowlists, HTTPS, secret storage)
- troubleshooting.md (symptom -> first check, common errors)
- recipes/zerto-pre-post-scripts.md (canonical use case)
- recipes/github-style-hmac.md (GitHub / Stripe-shaped webhooks)
- recipes/ad-password-reset.md (gMSA-backed self-service reset)
- recipes/ui-on-desktop.md (InteractiveUser pattern)

Top-level README.md restructured to point at docs/ as the source of
truth, dropping the duplicated installation snippets.

Installer ships docs/ alongside the binaries so they're available
offline at C:\Program Files\WebhookServer\docs\. GUI Help menu gains
a "Documentation" item that opens the docs site in a browser.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/README.md

@@ -0,0 +1,31 @@
+# Webhook Server documentation
+
+Webhook Server is a Windows service that runs a script (PowerShell, cmd, or any executable) when an HTTP request hits a URL you choose. It's designed for sysadmins who want to wire a tool like **Zerto pre/post scripts**, GitHub Actions, a monitoring system, or a backup tool into a Windows-side automation step — without writing a custom listener every time.
+
+## New here? Start with these
+
+1. [Concepts](concepts.md) — five-minute read on what a webhook is and how this server uses one
+2. [Installation](installation.md) — download, install, first endpoint
+3. [Recipe: Zerto pre/post scripts → AD / DNS update](recipes/zerto-pre-post-scripts.md) — the canonical reason this exists
+
+## Topical
+
+- [Upgrading](upgrading.md)
+- [Uninstalling](uninstalling.md)
+- [Run As modes — when to use which](runas-modes.md)
+- [Service account & Active Directory](service-account-and-ad.md)
+- [Network & security](network-and-security.md)
+- [Troubleshooting](troubleshooting.md)
+
+## Recipes (cookbook style)
+
+- [Zerto pre/post scripts → AD / DNS update](recipes/zerto-pre-post-scripts.md)
+- [GitHub-style HMAC-signed webhook](recipes/github-style-hmac.md)
+- [AD password reset endpoint](recipes/ad-password-reset.md)
+- [Pop UI on the user's desktop](recipes/ui-on-desktop.md)
+
+## Reference
+
+- [GitHub repo](https://github.com/recklessop/webhook-server)
+- [Latest release](https://github.com/recklessop/webhook-server/releases/latest)
+- [Issue tracker](https://github.com/recklessop/webhook-server/issues)