sa: add page (#3315)

pages/linux/sa.md

@@ -0,0 +1,16 @@
+# sa
+
+> Summarizes accounting information. Part of the acct package.
+> Shows commands called by users, including basic info on CPU time spent processing and I/O rates.
+
+- Display executable invocations per user (username not displayed):
+
+`sudo sa`
+
+- Display executable invocations per user, showing responsible usernames:
+
+`sudo sa --print-users`
+
+- List resources used recently per user:
+
+`sudo sa --user-summary`