Update Android README

Author: marcprux

swift-ci/sdks/android/README.md

@@ -25,11 +25,15 @@ Android NDK that will be used for cross-compilation.
 
 The `version` argument can be one of the following values:
 
-| version | Swift version |
+| version | Swift version example |
 | --- | --- |
 | `release` | swift-6.1-RELEASE |
-| `devel` | swift-6.2-DEVELOPMENT-SNAPSHOT-yyyy-mm-dd |
-| `trunk` | swift-DEVELOPMENT-SNAPSHOT-yyyy-mm-dd |
+| `swift-6.2-branch` | swift-6.2-DEVELOPMENT-SNAPSHOT-yyyy-mm-dd |
+| `development` | swift-DEVELOPMENT-SNAPSHOT-yyyy-mm-dd |
+
+> [!WARNING]
+> The workdir argument must not be located in a git repository (e.g., it cannot be the
+> current directory)
 
 ## Running
 
@@ -52,12 +56,11 @@ up the build. This can be useful, e.g., as part of a CI that
 validates a pull request, as building a single architecture
 takes around 30 minutes on a standard ubuntu-24.04 GitHub runner,
 whereas building for all the architectures takes over an hour.
-Building within a docker container increases this by about 50%.
 
 To build an artifactbundle for just the `x86_64` architecture, run:
 
 ```
-TARGET_ARCHS=aarch64 ./build-docker release /tmp/android-sdk
+TARGET_ARCHS=x86_64 ./build-docker release /tmp/android-sdk
 ```
 
 ## Installing and validating the SDK
@@ -66,7 +69,17 @@ The `.github/workflows/pull_request.yml` workflow
 will create and upload an installable SDK named something like:
 `swift-6.1-RELEASE_android-0.1.artifactbundle.tar.gz`
 
-The workflow will also install the SDK locally and use
+The GitHub workflow will also install the SDK locally and use
 [swift-android-action](https://github.com/marketplace/actions/swift-android-action)
 to build and test various Swift packages in an Android emulator using the
 freshly-created SDK bundle.
+
+## Building locally
+
+Instead of building within a Docker container, the script can also
+perform the build locally on an Ubuntu 24.04 machine with all the
+build prerequisites already installed. This will generate
+the same artifacts in approximately half the time, and
+may be suitable to an already containerized envrionment (such as
+a GitHub runner).
+