Add repo scaffolding to meet repository standards

Add .gitignore, LICENSE (MIT), Makefile, Dockerfile, .dockerignore,
and pin prettier via yarn lockfile for integrity-checked markdown
formatting. Update REPO_POLICIES.md self-reference to point to this
repo. Format markdown files with prettier.

Makefile

@@ -0,0 +1,21 @@
+.PHONY: test lint fmt fmt-check check docker
+
+PRETTIER := yarn run prettier
+
+test:
+	@echo "No tests defined."
+
+lint:
+	@echo "Linting markdown files..."
+	@$(PRETTIER) --check '**/*.md' --tab-width 4
+
+fmt:
+	@$(PRETTIER) --write '**/*.md' --tab-width 4
+
+fmt-check:
+	@$(PRETTIER) --check '**/*.md' --tab-width 4
+
+check: test lint fmt-check
+
+docker:
+	docker build -t prompts .