b4: Better describe how piem-b4-am-ready-from-mid gets the thread

piem-b4-am-ready-from-mid's docstring doesn't mention that it tries to
download the thread from a piem-inboxes URL before falling back to
letting b4 handle the download.  The manual's description is better,
though it makes it sound like the b4 fallback depends on not finding a
URL in piem-inboxes rather than the download being unsuccessful for
whatever reason.  Reword the docstring and manual text to hopefully
make things clearer.

Message-Id: <20210524005040.12668-1-kyle@kyleam.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/piem-b4.el b/piem-b4.el
index e76953e..ddb18d5 100644
--- a/piem-b4.el
+++ b/piem-b4.el
@@ -131,10 +131,15 @@ list of arguments specified via ARGS."
 (defun piem-b4-am-from-mid (mid &optional args toggle-worktree)
   "Get the thread for MID, extract an am-ready mbox, and apply it.
 
-Try to get a thread for the Message-Id MID with
-`piem-mid-to-thread-functions', falling back to letting b4
-download it.  After calling `b4 am' with ARGS to prepare an
-am-ready mbox, feed the result to `git am'.
+Try to generate a thread for the Message-Id MID with
+`piem-mid-to-thread-functions'.  If that fails, try to download
+the thread from the `piem-inboxes' URL associated with the
+current buffer, provided that the current buffer's message ID
+matches MID.  And if that doesn't work, let `b4 am' download the
+thread according to its own configuration.
+
+After calling `b4 am' with ARGS to prepare an am-ready mbox, feed
+the result to `git am'.
 
 When prefix argument TOGGLE-WORKTREE is non-nil, invert the
 meaning of `piem-am-create-worktree'.  With the default value,