feat: set up mutt with isync

GitOrigin-RevId: ed8952fc9d50e6268991c6082bf99bc6db4bf247
diff --git a/dot_mailcap b/dot_mailcap
new file mode 100644
index 0000000..15c9674
--- /dev/null
+++ b/dot_mailcap
@@ -0,0 +1 @@
+image/*; (clear && img2sixel %s); needsterminal