Explain NXS in plain English and add writing guidance

README.md

@@ -55,15 +55,18 @@ repositories {
 
 ## NetherNet and external signalling
 
-`transport-nethernet` provides the attributed NetherNet transport and local HTTP
-signalling integration. `external-signalling` implements the open
-[NetherNet External Signalling v1 contract](docs/external-signalling/README.md),
-including registration, background lifecycle and stateless admission.
-See [contribution provenance and intended submission slices](docs/contribution-provenance.md).
+`transport-nethernet` provides NetherNet transport and local HTTP signalling.
+`external-signalling` lets a host register with its chosen provider and check
+client connection tokens locally. Read the
+[NXS v1 specification](docs/external-signalling/README.md) and the
+[contribution history and proposed upstream PRs](docs/contribution-provenance.md).
 
 Build the pinned native development chain with `bash scripts/bootstrap-native-admission.sh`,
 then run `./gradlew --max-workers=2 build :external-signalling:nativeAdmissionTest`.
 An existing local Maven repository can be selected with
 `-PnativeMavenRepository=/absolute/path/to/maven`. The development native artifacts
-currently target Linux x86_64 and system OpenSSL; cross-platform release packaging
-remains a separate release gate.
+currently target Linux x86_64 and system OpenSSL. Other platforms need their own
+release builds and tests.
+
+When editing documentation or PR descriptions, follow the
+[technical-writing checklist](docs/technical-writing.md).