Add task for `tcardgen`.

tasks/tcardgen.rake

@@ -0,0 +1,7 @@
+#!/usr/bin/env rake
+
+desc 'Generate OGP images'
+task :tcard do
+  sh 'find static/ogp/ -type f -name "*.png" | grep -v "base.png" | xargs -t --no-run-if-empty rm'
+  sh 'find content/ -type f -name "*.md" | xargs -t -I % tcardgen -f ~/repo/sample-font/ -o static/ogp/ -c config/tcardgen.yaml %'
+end