Apply suggestions from Tom's code review

Co-authored-by: Tom Sellman <[email protected]>

Author: robsyme

Makefile

@@ -75,7 +75,7 @@ publish-index:
 #
 install-plugin:
 ifdef plugin
-	./gradlew installSpecificPlugin -Pplugin=${plugin}
+	./gradlew :plugins:${plugin}:installPlugin
 else
-	./gradlew installPlugins
+	./gradlew installPlugin
 endif

README.md

@@ -108,10 +108,10 @@ The plugin can be tested without using a local Nextflow build using the followin
    Alternatively, you can use Gradle commands directly:
    ```bash
    # Install a specific plugin
-   ./gradlew installSpecificPlugin -Pplugin=nf-hello
+   ./gradlew :plugins:nf-hello:installPlugin
 
    # Install all plugins
-   ./gradlew installPlugins
+   ./gradlew installPlugin
    ```
 
 3. Create a pipeline that uses your plugin and run it: `nextflow run ./my-pipeline-script.nf`