Add note about updating .xcode-version in Buildkite pipelines

https://github.com/wordpress-mobile/WordPress-iOS/pull/19793/files#r1052892161

Author: mokagio

.buildkite/cache-builder.yml

@@ -13,6 +13,7 @@ common_params:
         repo: "wordpress-mobile/wordpress-ios/"
   # Common environment values to use with the `env` key.
   - &common_env
+    # Be sure to also update the `.xcode-version` file when updating the Xcode image/version here
     IMAGE_ID: xcode-14.2
 
 steps:

.buildkite/pipeline.yml

@@ -8,6 +8,7 @@ common_params:
         repo: "wordpress-mobile/wordpress-ios/"
   # Common environment values to use with the `env` key.
   - &common_env
+    # Be sure to also update the `.xcode-version` file when updating the Xcode image/version here
     IMAGE_ID: xcode-14.2
 
 # This is the default pipeline – it will build and test the app

.buildkite/release-builds.yml

@@ -10,6 +10,7 @@ common_params:
         repo: "wordpress-mobile/wordpress-ios/"
   # Common environment values to use with the `env` key.
   - &common_env
+    # Be sure to also update the `.xcode-version` file when updating the Xcode image/version here
     IMAGE_ID: xcode-14.2
 
 steps: