migrate to pnpm

.github/workflows/build.yml

@@ -20,14 +20,20 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
+
+    - name: Setup pnpm
+      uses: pnpm/action-setup@646cdf48217256a3d0b80361c5a50727664284f2
+
     - name: Use Node.js
       uses: actions/setup-node@v2
       with:
         node-version: '16'
         check-latest: false
-    - run: npm ci
-    - run: npm run build --if-present
-    - run: npm run test-with-coverage
+        cache: pnpm
+
+    - run: pnpm install
+    - run: pnpm run build --if-present
+    - run: pnpm run test-with-coverage
       if: "!contains(github.event.head_commit.message, 'skip test')"
 
     - name: Deploy to github pages

Styleguide.md

@@ -0,0 +1,6 @@
+# Styleguide
+
+1. Use the `Loading` class for lazy loaded placeholders.
+2. If you need to update a component's state based on the previous state, use callbacks.
+3. There's a top-down structure. Children should not know anything about their parents.
+   - Methods will be so useful when I extract `Sudoku` somewhere else