Add contributing and packaging instructions

CONTRIBUTING.md

+Development And Contributing Instructions
+=========================================
+
+Creating a Python package
+-------------------------
+
+:memo: TODO: add instructions for packaging for plain Python!
+
+Making a new release via Maven
+------------------------------
+
+To create a new release, clone the [scijava-scripts][gh_scijava-scripts] repo
+(e.g. in `/opt/imagej/`) and run the `release-version.sh` helper:
+
+```bash
+BASE_DIR=/opt/imagej
+mkdir -pv "$BASE_DIR"
+cd "$BASE_DIR"
+git clone https://github.com/scijava/scijava-scripts
+cd -
+
+RELEASE_SCRIPT="$BASE_DIR/scijava-scripts/release-version.sh"
+
+$RELEASE_SCRIPT --skip-push --skip-gpg --skip-license-update
+```
+
+Build & Deploy with Maven using Visual Studio Code
+--------------------------------------------------
+
+Building and deploying the package can be greatly simplified using "tasks" in
+[Visual Studio Code][www_vscode]. By adding the following settings to the
+`.vscode/tasks.json` file, you can simply press `Ctrl+Shift+B` in VS Code and
+select the *deploy* task for running Maven and have the resulting JAR file being
+placed in `/opt/fiji-packaging/Fiji.app/jars/` (adjust to your path as
+necessary):
+
+```json
+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "verify",
+            "type": "shell",
+            "command": "mvn -B verify",
+            "group": "build"
+        },
+        {
+            "label": "test",
+            "type": "shell",
+            "command": "mvn -B test",
+            "group": "test"
+        },
+        {
+            "label": "deploy",
+            "type": "shell",
+            "command": "mvn -Dimagej.app.directory=/opt/fiji-packaging/Fiji.app",
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            },
+            "problemMatcher": []
+        }
+    ]
+}
+```
+
+[gh_scijava-scripts]: https://github.com/scijava/scijava-scripts
+[www_vscode]: https://code.visualstudio.com/