direnv: make args explicit so its easy to change

for direnv enjoyers

Signed-off-by: William Casarin <jb55@jb55.com>

.envrc

@@ -1,4 +1,8 @@
-use nix
+# set to false if you don't care to include android stuff
+export use_android=true
+export android_emulator=false
+
+use nix --arg use_android $use_android --arg android_emulator $android_emulator
 
 export PATH=$PATH:$HOME/.cargo/bin
 export JB55=32e1827635450ebb3c5a7d12c1f8e7b2b514439ac10a67eef3d9fd9c5c68e245