airpaste: add page (#1882)

pages/common/airpaste.md

@@ -0,0 +1,15 @@
+# airpaste
+
+> Share messages and files on the same network.
+
+- Send file:
+
+`airpaste < {{file.txt}}`
+
+- Receive file:
+
+`airpaste > {{file.txt}}`
+
+- Create/Join channel:
+
+`airpaste {{channel_name}}`