Say in the go and nodejs READMEs what holds at this step, and what holds once the users require them (review of issue 1573 step A)

modules/nodejs/README.md

@@ -2,11 +2,13 @@
 
 Node.js and npm as a module (novox/hq ADR 0477 §4, issue 1573).
 
-- **Owns the packages `nodejs` and `npm`.** No other module declares them (`checks/toolchains` refuses one that
-  does).
-- **Provides `node-toolchain` with the machine's reach**: dev-tools, lab and mesh-build-node require it, and the
-  requirement is met only by this module on the same machine. It is never pulled in for whatever asked, so
-  `nodejs` is assigned to a node on purpose, and a node without it refuses a module that needs it at resolution.
+- **Declares the packages `nodejs` and `npm`.** Today dev-tools, lab and mesh-build-node declare some of them too,
+  which the resolver allows (ADR 0303); once they require `node-toolchain` instead (issue 1573's second step), this
+  is the only module that declares them, and `checks/toolchains` refuses another.
+- **Provides `node-toolchain` with the machine's reach**: a module that requires it composes only on a machine where
+  this module is assigned. It is never pulled in for whatever asked, so `nodejs` is assigned to a node on purpose.
+  Nothing requires it yet; dev-tools, lab and mesh-build-node will, in the second step.
 - Holds no long-running resource, so it adds nothing to `health-undeclared`.
 
-The node-engine never uninstalls a package, so moving the declaration here removes nothing from a node.
+The node-engine never uninstalls a package, so when the users stop declaring `nodejs` and `npm`, nothing leaves a
+node that has this module.