Use swift/main for development

Author: milseman

README.md

@@ -39,11 +39,7 @@ Specifically, `_RegexParser` contains the parser for regular expression literals
 
 ### Branching scheme
 
-#### Development branch
-
-The `main` branch is the branch for day-to-day development. Generally, you should create PRs against this branch.
-
-#### Swift integration branches
+The `swift/main` branch is the branch for day-to-day development. Generally, you should create PRs against this branch.
 
 Branches whose name starts with `swift/` are Swift integration branches similar to those in [apple/llvm-project](https://github.com/apple/llvm-project). For each branch, dropping the `swift/` prefix is the corresponding branch in [apple/swift](https://github.com/apple/swift).
 
@@ -55,15 +51,17 @@ Branches whose name starts with `swift/` are Swift integration branches similar
 
 A pair of corresponding branches are expected to build successfully together and pass all tests.
 
-### Integration workflow
+### Running Package CI and full Swift CI
 
 To integrate the latest changes in apple/swift-experimental-string-processing to apple/swift, carefully follow the workflow: 
 
-- Create pull requests.
-  - Create a branch from a commit on `main` that you would like to integrate into `swift/main`.
-  - Create a pull request in apple/swift-experimental-string-processing from that branch to `swift/main`, e.g. "[Integration] main (<commit>) -> swift/main".
+- Run package CI
+  - In the pull request, trigger package CI using
+```
+@swift-ci please test
+```
+- Run full Swift CI for any changes to public or SPI interfaces or the `_RegexParser` module.
   - If apple/swift needs to be modified to work with the latest `main` in apple/swift-experimental-string-processing, create a pull request in apple/swift.  **Note:** Since CI in apple/swift-experimental-string-processing has not yet been set up to run full toolchain tests, you should create a PR in apple/swift regardless; if the integartion does not require changing apple/swift, create a dummy PR in apple/swift by changing the README and just not merge it in the end.
-- Trigger CI.
   - In the apple/swift-experimental-string-processing pull request, trigger CI using the following command (replacing `<PR NUMBER>` with the apple/swift pull request number, if any):
     ```
     apple/swift#<PR NUMBER> # use this line only if there is an corresponding apple/swift PR
@@ -75,7 +73,9 @@ To integrate the latest changes in apple/swift-experimental-string-processing to
     @swift-ci please test
     ```
 - Merge when approved.
-  - Merge the pull request in apple/swift-experimental-string-processing as a **merge commit**.
+  - Merge the PR in apple/swift-experimental-string-processing:
+    - as a squash or rebase if against swift/main (the development branch).
+    - as a merge commit if it's a merge from swift/main to swift/release/x.y.
   - Merge the pull request in apple/swift (if any).
 
 ### Development notes