Merge pull request swiftlang#31 from allevato/dev-docs

Add development advice for keeping the pipeline and test manifest up-to-date.

Author: allevato

Documentation/Development.md

@@ -1,5 +1,31 @@
 # Developing `swift-format`
 
+## Keeping the Pipeline and Tests Updated
+
+Since Swift does not yet have a runtime reflection system, we use code
+generation to keep the linting/formatting pipeline up-to-date. If you add or
+remove any rules from the `SwiftFormatRules` module, or if you add or remove
+any `visit` methods from an existing rule in that module, you must run the
+`generate-pipeline` tool update the pipeline and configuration sources.
+
+The easiest way to do this is to run the following command in your terminal:
+
+```shell
+swift run generate-pipeline
+```
+
+If successful, this tool will update
+`Sources/SwiftFormatConfiguration/RuleRegistry+Generated.swift` and
+`Sources/SwiftFormat/Pipelines+Generated.swift`.
+
+Likewise, you should keep the Linux XCTest manifests updated if you add or
+remove any tests from `swift-format` by running the following command in your
+terminal:
+
+```shell
+swift test --generate-linuxmain
+```
+
 ## Command Line Options for Debugging
 
 `swift-format` provides some hidden command line options to facilitate