Clean up Java readme

Author: headius

java/README.md

@@ -6,20 +6,57 @@ This is the top-level project for the Java API and backend bindings for the Pris
 * native/ contains a native binding for the Prism shared library
 * wasm/ contains a Chicory-based WASM build and binding
 
+## Building the Java components
+
+Some files need to be generated before the Maven artifacts can build:
+
+### Templated sources
+
+Sources under `api` are generated from templates in `../templates`. Those sources are generated using the follow command line:
+
+```
+$ PRISM_EXCLUDE_PRETTYPRINT=1 PRISM_SERIALIZE_ONLY_SEMANTICS_FIELDS=1 bundle exec rake templates
+```
+
+The files go under `api/target/generated-sources/java` and will be removed with `mvn clean`.
+
+### WASM build of Prism
+
+The `wasm` project needs a WASM build of Prism to be generated with the following command:
+
+```
+$ make java-wasm WASI_SDK_PATH=<path to WASI sdk>
+```
+
+The files go under `wasm/target/generated-sources/wasm` and will be removed with `mvn clean`.
+
+### Build and install
+
+The projects can be built and installed into a local Maven repository by running the following command:
+
+```
+$ mvn install
+```
+
 ## Updating versions
 
 Run the following command to update all module versions:
 
 ```
-mvn versions:set -DnewVersion=1.2.3-SNAPSHOT
+$ mvn versions:set -DnewVersion=1.2.3-SNAPSHOT
 ```
 
 ## Releasing
 
-Snapshots can be deployed with `mvn deploy` while the versions are `-SNAPSHOT`.
+Snapshots can be deployed to the Maven snapshot repository while the versions end with `-SNAPSHOT`:
 
-When releasing to Maven Central, all projects should be released together using the `release` profile:
+```
+$ mvn deploy
+```
+
+When releasing to Maven Central, all projects should be released together using the `release` profile, which will use the local default GPG key to sign the packages:
 
 ```
-mvn clean deploy -Prelease
+$ mvn deploy -Prelease
 ```
+