👷 Adds an action to cache artifacts, to speed up build

.github/workflows/cache-artifacts.yml

@@ -0,0 +1,13 @@
+# Caches artifacts, including NPM dependencies, to speed up build times
+name: Caching Primes
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/cache@v2
+      with:
+        path: ~/.npm
+        key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}
+        restore-keys: |
+          ${{ runner.os }}-node-