Bump to 1.0.0-alpha.1 (#36)

Bump to 1.0.0-alpha.1

### Motivation

Prepare for 1.0.0-alpha.1.

### Modifications

- Updated runtime dependency.
- Updated docs.

### Result

Ready to tag 1.0.0-alpha.1.

### Test Plan

All tests pass.


Reviewed by: simonjbeaumont

Builds:
     ✔︎ pull request validation (5.10) - Build finished. 
     ✔︎ pull request validation (5.9) - Build finished. 
     ✔︎ pull request validation (nightly) - Build finished. 
     ✔︎ pull request validation (soundness) - Build finished. 

#36

Package.swift

@@ -41,7 +41,7 @@ let package = Package(
         ),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-openapi-runtime", branch: "main"),
+        .package(url: "https://github.com/apple/swift-openapi-runtime", exact: "1.0.0-alpha.1"),
         .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
         .package(url: "https://github.com/apple/swift-collections", from: "1.0.0"),
     ],

README.md

@@ -25,7 +25,7 @@ Add the package dependency in your `Package.swift`:
 ```swift
 .package(
     url: "https://github.com/apple/swift-openapi-urlsession",
-    .upToNextMinor(from: "0.3.0")
+    exact: "1.0.0-alpha.1"
 ),
 ```
 

Sources/OpenAPIURLSession/Documentation.docc/Documentation.md

@@ -25,7 +25,7 @@ Add the package dependency in your `Package.swift`:
 ```swift
 .package(
     url: "https://github.com/apple/swift-openapi-urlsession",
-    .upToNextMinor(from: "0.3.0")
+    exact: "1.0.0-alpha.1"
 ),
 ```