Update help text

Author: owenv

Sources/Commands/SwiftPackageTool.swift

@@ -296,8 +296,9 @@ extension SwiftPackageTool {
  The experimental-api-diff command can be used to compare the Swift API of \
  a package to a baseline revision, diagnosing any breaking changes which have \
  been introduced. By default, it compares every Swift module from the baseline \
- revision which is part of a library product. If this behavior is undesirable, \
- the `--product` and `--target` options can be used to restrict the scope of \
+ revision which is part of a library product. For packages with many targets, this \
+ behavior may be undesirable as the comparison can be slow. \
+ The `--products` and `--targets` options may be used to restrict the scope of \
  the comparison.
  """)