Document publishing steps.

Author: kishorenc

CONTRIBUTING.md

@@ -29,3 +29,26 @@ Before making a PR to this repository look out for the following guidelines.
 
 **NOTE**: The `model` directory is **read-only** make sure not to edit it.
 
+## Publishing
+
+Publishing requires the presence of a `~/.gradle.properties` file:
+
+```shell
+signing.keyId=x1234567
+signing.password=
+signing.secretKeyRingFile=/Users/user/.gnupg/secring.gpg
+
+sonatypeUsername=xxxxxx
+sonatypePassword=
+```
+
+The `secring.gpg` file can be generated with:
+
+```shell
+gpg --keyring secring.gpg --export-secret-keys > ~/.gnupg/secring.gpg
+```
+
+```shell
+./gradlew publishToSonatype closeAndReleaseSonatypeStagingRepository
+```
+