mailx: various tweaks

- restore "content" as opposed to "body", per PR discussion
- various improvements to command descriptions

pages/common/mailx.md

@@ -2,15 +2,15 @@
 
 > Send and receive mail.
 
-- To send mail, the body is typed after the command and ended with Control-D:
+- Send mail (the content should be typed after the command, and ended with Control-D):
 
 `mailx -s "{{subject}}" {{to_addr}}`
 
-- Send mail with a short body:
+- Send mail with content passed from another command:
 
 `echo "{{content}}" | mailx -s "{{subject}}" {{to_addr}}`
 
-- Send mail with a body from a file:
+- Send mail with content read from a file:
 
 `mailx -s "{{subject}}" {{to_addr}} < {{content.txt}}`
 
@@ -18,7 +18,7 @@
 
 `mailx -s "{{subject}}" -c {{cc_addr}} {{to_addr}}`
 
-- Send mail and set sender address:
+- Send mail specifying the sender address:
 
 `mailx -s "{{subject}}" -r {{from_addr}} {{to_addr}}`