Add script `speedup`

diff --git a/speedup b/speedup
new file mode 100755 (executable)
index 0000000..6e91eee
--- /dev/null
+++ b/speedup
@@ -0,0 +1,6 @@
+#! /bin/sh
+# See https://stackoverflow.com/a/24045966/7976758
+
+git config --global core.preloadindex true &&
+git config --global core.fscache true &&
+exec git config --global gc.auto 256