migrates documentation/continuousintegration.md (#8760)

### Motivation:

migrates content from documentation/continuousintegration.md

### Modifications:

- convert to DocC format
- minor wording and format adjustments

resolves #8587

---------

Co-authored-by: Bri Peticca <briannap_22@apple.com>

Author: heckj

Sources/PackageManagerDocs/Documentation.docc/ContinuousIntegration.md

@@ -0,0 +1,39 @@
+# Continuous Integration Workflows
+
+Build Swift packages with an existing continuous integration setup and prepare apps that consume package dependencies within an existing CI pipeline.
+
+## Overview
+
+*Continuous integration* (*CI*) is the process of automating and streamlining the building, analyzing, testing, archiving, and publishing of your apps to ensure that they're always in a releasable state.
+Most projects that contain or depend on Swift packages don't require additional configuration.
+
+## Use the Expected Version of a Package Dependency
+
+To ensure a CI workflow’s reliability, verify it uses the appropriate version of package dependencies.
+SwiftPM records the result of dependency resolution in the file `Package.resolved`, at the top-level of the package.
+When available, it's used when performing dependency resolution.
+
+Run <doc:PackageUpdate> to update dependencies to the latest eligible versions and update `Package.resolved`.
+For more information on resolving and updating dependencies, see <doc:ResolvingPackageVersions>.
+
+
+## Provide Credentials
+
+To resolve package dependencies that require authentication, such as private packages, provide credentials to your CI setup.
+Package manager honors the machine's SSH configuration - there's no additional setup required.
+For private package, use the SSH-based Git URLs and configure SSH credentials.
+You may also need to set up a `known_hosts` file in the `~/.ssh` directory of the user that runs your CI tasks.
+
+CI services like [Jenkins](https://www.jenkins.io/doc/book/using/using-credentials), [Github Action](https://docs.github.com/en/free-pro-team@latest/actions/reference/authentication-in-a-workflow), [TravisCI](https://docs.travis-ci.com/user/private-dependencies), and [CircleCI](https://circleci.com/docs/2.0/gh-bb-integration/#security) provide ways to set up SSH keys or other techniques to access private repositories.
+Since Package manager uses git to clone the repositories there's no additional setup required; Package manager honors the machine's SSH and Git configuration.
+
+## Using xcodebuild
+
+When building on macOS based CI hosts you can use the command-line tool `xcodebuild`.
+`xcodebuild` uses Xcode's built-in Git tooling to connect to repositories.
+
+In many cases, you don't need to make changes to how xcodebuild connects to them.
+However, some use cases require you use the git configuration — for example URL remapping, the use of proxies, or advanced SSH configurations.
+To have xcodebuild use your Mac's Git installation and configuration instead of Xcode's built-in Git tooling, pass `-scmProvider system` to the xcodebuild command.
+
+For more information on using xcodebuild in continuous integration workflows, visit [Building Swift packages or apps that use them in continuous integration workflows](https://developer.apple.com/documentation/swift_packages/building_swift_packages_or_apps_that_use_them_in_continuous_integration_workflows).

Sources/PackageManagerDocs/Documentation.docc/Documentation.md

@@ -29,6 +29,7 @@ The Swift Package Manager lets you share your code as a package, depend on and u
 - <doc:SwiftVersionSpecificPackaging>
 - <doc:BundlingResources>
 - <doc:ReleasingPublishingAPackage>
+- <doc:ContinuousIntegration>
 - <doc:UsingShellCompletion>
 - <doc:SwiftPMAsALibrary>
 - <doc:ModuleAliasing>