Moved system package inputs out to top level (#4406)

plugins/inputs/mem/README.md

@@ -0,0 +1,35 @@
+# Mem Input Plugin
+
+The mem plugin collects system memory metrics.
+
+For a more complete explanation of the difference between *used* and
+*actual_used* RAM, see [Linux ate my ram](http://www.linuxatemyram.com/).
+
+### Configuration:
+```toml
+# Read metrics about memory usage
+[[inputs.mem]]
+  # no configuration
+```
+
+### Metrics:
+
+- mem
+  - fields:
+  	- active (int)
+  	- available (int)
+  	- buffered (int)
+  	- cached (int)
+  	- free (int)
+  	- inactive (int)
+  	- slab (int)
+  	- total (int)
+  	- used (int)
+  	- available_percent (float)
+  	- used_percent (float)
+  	- wired (int)
+
+### Example Output:
+```
+mem cached=7809495040i,inactive=6348988416i,total=20855394304i,available=11378946048i,buffered=927199232i,active=11292905472i,slab=1351340032i,used_percent=45.43883523785713,available_percent=54.56116476214287,used=9476448256i,free=1715331072i 1511894782000000000
+```