* mu4e: improve docs for capturing / attaching message (and set them to message/rfc822)

mu4e/mu4e-compose.el

@@ -86,7 +86,8 @@ forwarded or edited) in `mu4e-compose-pre-hook.")
 
 
 (defun mu4e-compose-attach-captured-message ()
-  "Insert the last captured message file as an attachment."
+  "Insert the last captured message (through
+`mu4e-action-capture-message') file as an attachment."
     (interactive)
   (unless mu4e-captured-message
     (mu4e-warn "No message has been captured"))
@@ -95,7 +96,7 @@ forwarded or edited) in `mu4e-compose-pre-hook.")
       (mu4e-warn "Captured message file not found"))
     (mml-attach-file
       path
-      "application/octet-stream"
+      "message/rfc822"
       (or (plist-get mu4e-captured-message :subject) "No subject")
       "attachment")))
 
@@ -566,8 +567,7 @@ a file which our backend has conveniently saved for us (as a
 tempfile).
 
 The name of the draft folder is constructed from the concatenation
- of `mu4e-maildir' and `mu4e-drafts-folder' (therefore, these must be
- set).
+ of `mu4e-maildir' and `mu4e-drafts-folder' (these must be set).
 
 The message file name is a unique name determined by
 `mu4e-send-draft-file-name'.

mu4e/mu4e.texi

@@ -677,9 +677,10 @@ maildir:/bar(saTF)}.
 on the message at point. You can specify these actions using the variable
 @code{mu4e-headers-actions}. Refer to @ref{Actions} for details.
 
-@t{mu4e} defines some default actions - one is @t{capture} - @key{a c} will
-'capture' the current message. Next, when you're editing some message, you can
-include the previously captured message as an attachment, using
+@t{mu4e} defines some default actions. One of this those is for
+@emph{capturing} a message: @key{a c} will 'capture' the current
+message. Next, when you're editing some message, you can include the
+previously captured message as an attachment, using
 @code{mu4e-compose-attach-captured-message}.
 
 The file @file{mu4e-actions.el} in the @t{mu4e} source distribution contains a