Document collecting log output

Redirecting stdout writes log output to that file, but this wasn't
easily discoverable.

v2 removes changes to aerc-tutorial; I was also on the fence about that,
and agree that it isn't on-topic for the tutorial.

Addresses https://todo.sr.ht/~sircmpwn/aerc2/180

README.md

@@ -23,6 +23,10 @@ Then compile aerc:
 On its first run, aerc will copy the default config files to `~/.config/aerc`
 and show the account configuration wizard.
 
+If you redirect stdout to a file, logging output will be written to that file:
+
+    $ aerc > log
+
 ## Resources
 
 [Send patches](https://git-send-email.io) and questions to

doc/aerc.1.scd

@@ -132,6 +132,14 @@ message list, the message in the message viewer, etc).
 *close*
 	Closes the terminal.
 
+# LOGGING
+
+Aerc does not log by default, but collecting log output can be useful for
+troubleshooting and reporting issues. Redirecting stdout when invoking aerc will
+write log messages to that file:
+
+	$ aerc > log
+
 # SEE ALSO
 
 *aerc-config*(5) *aerc-imap*(5) *aerc-smtp*(5) *aerc-tutorial*(7)