mailx: Improve the readability of the descriptions

pages/common/mailx.md

@@ -2,15 +2,15 @@
 
 > Send and receive mail.
 
-- To send mail, the content is typed after the command and ended with Control-D:
+- To send mail, the body is typed after the command and ended with Control-D:
 
 `mailx -s "{{subject}}" {{to_addr}}`
 
-- Send mail with short content:
+- Send mail with a short body:
 
 `echo "{{content}}" | mailx -s "{{subject}}" {{to_addr}}`
 
-- Send mail with content which written in a file:
+- Send mail with a body from a file:
 
 `mailx -s "{{subject}}" {{to_addr}} < {{content.txt}}`