Add docs about how newlines is not great here

morph/grid/local/README.rst

@@ -53,6 +53,11 @@ Generate your own like this::
   [nix-shell:~/PrivateStorageio]$ PaymentServer-generate-key
   SILOWzbnkBjxC1hGde9d5Q3Ir/4yLosCLEnEQGAxEQE=
 
+Make sure you write it into the key file `without any leading or trailing white space, also without newlines <https://github.com/LeastAuthority/python-challenge-bypass-ristretto/issues/37>`_.
+For example::
+
+  echo -n "SILOWzbnkBjxC1hGde9d5Q3Ir/4yLosCLEnEQGAxEQE=" > ristretto.signing-key
+
 For the Stripe key any random bytes with a little light formatting "work" - at least to make our software happy - but if you want to be able to interact with Stripe and have payments (even pretend payments) move all the way through the system you should get a Stripe account and generate a key w/ them.
 Lauri can get you added to our "dev" Stripe account, too, though I forget how important that is for ad hoc dev/testing.