Update docs, remove plugin

Package.swift

@@ -22,19 +22,12 @@ let package = Package(
     products: [
         .executable(name: "validate-spi-manifest", targets: ["validate-spi-manifest"]),
         .library(name: "SPIManifest", targets: ["SPIManifest"]),
-        .plugin(name: "SPIManifestValidatorPlugin", targets: ["ValidatorPlugin"])
     ],
     dependencies: [
         .package(url: "https://github.com/jpsim/Yams.git", "4.0.0"..<"6.0.0"),
     ],
     targets: [
         .executableTarget(name: "validate-spi-manifest", dependencies: ["SPIManifest"]),
-        .plugin(
-            name: "ValidatorPlugin",
-            capability: .command(intent: .custom(verb: "validate-spi-manifest",
-                                                 description: "Validate a .spi.yml file")),
-            dependencies: ["validate-spi-manifest"]
-        ),
         .target(name: "SPIManifest", dependencies: ["Yams"]),
         .testTarget(name: "SPIManifestTests", dependencies: ["SPIManifest"]),
     ]

Sources/SPIManifest/Documentation.docc/CommonUseCases.md

@@ -4,7 +4,6 @@ The contents of a `.spi.yml` file allow package authors to configure their packa
 
 The following are some common use cases.
 
-
 ## Host DocC documentation in the Swift Package Index
 
 Package authors can configure their package's documentation to be hosted on the Swift Package Index. In order to do so, add a `.spi.yml` file with the following content to the root of your package repository listing one or more targets you want to generate documentation for:

Sources/SPIManifest/Documentation.docc/ManifestValidation.md

@@ -0,0 +1,49 @@
+# Manifest Validation
+
+How to validate `.spi.yml` files.
+
+## Overview
+
+The easiest way to validate a `.spi.yml` is via the [Online Validator](https://swiftpackageindex.com/validate-spi-manifest) on the [Swift Package Index website](https://swiftpackageindex.com).
+
+You can also use the `validate-spi-manifest` executable to validate your `.spi.yml` file.
+
+### Online Validator
+
+The [Online Validator](https://swiftpackageindex.com/validate-spi-manifest) is a simple web form where you can submit your sample `.spi.yml` file and it will run the exact same parser as during package processing.
+
+The validator will display the parsed result or error messages if it fails.
+
+![](online-validator.png)
+
+### Validation Executable
+
+#### Installation
+
+You can build and install the validation executable by cloning this package and running `make install`:
+
+```sh
+git clone https://github.com/SwiftPackageIndex/SPIManifest.git && cd SPIManifest
+make install
+```
+
+This will copy the executable to `/usr/local/bin/`. To uninstall it, run
+
+```sh
+make uninstall
+```
+
+You can also install it using [Mint](https://swiftpackageindex.com/yonaskolb/Mint):
+
+```sh
+mint install SwiftPackageIndex/SPIManifest
+```
+
+#### Validation with the Executable
+
+Once installed, you can run the executable with the path to an `.spi.yml` to validate it:
+
+```sh
+❯ validate-spi-manifest ~/Projects/MyPackage/.spi.yml 
+✅ The file is valid.
+```

Sources/SPIManifest/Documentation.docc/SPIManifest.md

@@ -18,9 +18,9 @@ Here are some examples of things that can be configured by this file:
 
 ### Validation
 
-This package comes with an executable to validate your `.spi.yml` for correctness. See
+Swift Package Index manifests can be validated for correctness via the [Online Validator](https://swiftpackageindex.com/validate-spi-manifest) or via an executable that comes with this package. See
 
-- <doc:Validation>
+- <doc:ManifestValidation>
 
 for more details.
 
@@ -29,5 +29,6 @@ for more details.
 ### Essentials
 
 - <doc:CommonUseCases>
+- <doc:ManifestValidation>
 - <doc:Validation>
 - ``Manifest``