docs(readme): give the download-and-verify path a PowerShell form (#85)

"Downloading without cloning" was bash only, in the README of a PowerShell
toolkit. It is also the first thing a stranger does, so the one section aimed
squarely at newcomers was the one they could not run: `sha256sum` and `unzip`
are not Windows commands at all, and `&&` is a parse error in PowerShell 5.1
rather than a wrong result.

PowerShell goes first here, because these commands are PowerShell - Get-FileHash
against the .sha256, Expand-Archive, then zchecksums.cmd for the contents. The
bash form stays below it, matching how "Verifying what you downloaded" already
leads with zchecksums and offers sha256sum second.

Tested against releases/zscripts-v1.0.0.0.9.zip: the comparison returns True.
It also gets a note, because the output invites a wrong conclusion -
Get-FileHash prints upper case and the .sha256 file holds lower, so the two
strings look different side by side. PowerShell's -eq is case-insensitive on
strings, so the check is right and the eyes are wrong.

Twins regenerated; the Pester twin-sync test passes.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -411,6 +411,24 @@ Verification walks its channels in trust order — docker-network `viaProxy`, th
 
 Each release is packaged as a zip in [`releases/`](releases/) — grab the latest `zscripts-v*.zip`, check it, unzip, done:
 
+**Windows · PowerShell** — these commands are a PowerShell toolkit, so this is
+most people's path. `sha256sum` and `unzip` are not Windows commands:
+
+```powershell
+$zip = "zscripts-v1.0.0.0.0.zip"
+(Get-FileHash $zip -Algorithm SHA256).Hash -eq (Get-Content "$zip.sha256").Split()[0]   # True = good
+Expand-Archive $zip -DestinationPath zscripts
+cd zscripts
+.\zchecksums.cmd                                                                        # verify the contents
+```
+
+`Get-FileHash` prints the hash in **upper** case and the `.sha256` file holds it
+in lower — they look different side by side and are not. `-eq` on strings is
+case-insensitive in PowerShell, so the comparison above is right; trust the
+`True`, not your eyes.
+
+**macOS · Linux · Git Bash · WSL**
+
 ```bash
 sha256sum -c zscripts-v1.0.0.0.0.zip.sha256   # verify the download
 unzip zscripts-v1.0.0.0.0.zip -d zscripts     # extract

README.txt

@@ -384,6 +384,22 @@ Downloading without cloning
 
 Each release is packaged as a zip in releases/ (releases/) — grab the latest zscripts-v*.zip, check it, unzip, done:
 
+Windows · PowerShell — these commands are a PowerShell toolkit, so this is
+most people's path. sha256sum and unzip are not Windows commands:
+
+    $zip = "zscripts-v1.0.0.0.0.zip"
+    (Get-FileHash $zip -Algorithm SHA256).Hash -eq (Get-Content "$zip.sha256").Split()[0]   # True = good
+    Expand-Archive $zip -DestinationPath zscripts
+    cd zscripts
+    .\zchecksums.cmd                                                                        # verify the contents
+
+Get-FileHash prints the hash in upper case and the .sha256 file holds it
+in lower — they look different side by side and are not. -eq on strings is
+case-insensitive in PowerShell, so the comparison above is right; trust the
+True, not your eyes.
+
+macOS · Linux · Git Bash · WSL
+
     sha256sum -c zscripts-v1.0.0.0.0.zip.sha256   # verify the download
     unzip zscripts-v1.0.0.0.0.zip -d zscripts     # extract
     cd zscripts && sha256sum -c CHECKSUMS.txt     # verify the contents