Add script to import strings, and doc.

Add GitHub action to sync strings.

.github/workflows/sync-from-external-sources.yml

@@ -0,0 +1,25 @@
+name: Sync Data From External Sources
+on:
+  schedule:
+    # Every nights at 6
+    - cron: "0 6 * * *"
+
+jobs:
+  sync-strings:
+    runs-on: ubuntu-latest
+    # Skip in forks
+    if: github.repository == 'vector-im/element-x-android'
+    # No concurrency required, runs every time on a schedule.
+    steps:
+      - uses: actions/checkout@v3
+      - name: Run local script
+        run: ./tools/strings/importStringsFromElement.sh
+      - name: Create Pull Request
+        uses: peter-evans/create-pull-request@v4
+        with:
+          commit-message: Import strings from Element Android
+          title: Sync strings
+          body: |
+            - Update strings from Element Android
+          branch: sync-strings
+          base: develop