add comment about SOAR_PYTHON_ABI3

Core/ClientSMLSWIG/Python/pyproject.toml

@@ -127,6 +127,7 @@ skip = [
 #
 # We pick python 3.9, since macOS ARM64 doesn't have 3.8, and so this is the earliest version on all platforms.
 build = "cp39*"
+# Inside CIs, we want to build the limited API, as we control SWIG's version there, so we opt-in.
 environment = { SOAR_PYTHON_ABI3="1" }
 # This test command:
 #  - imports soar_sml