Improve documentation.

plugins/inputs/nfsclient/README.md

@@ -1,14 +1,39 @@
 # Telegraf plugin: NFSCLIENT
 
 #### Plugin arguments:
-- **fullstat** bool: Collect per-operation statistics
+- **fullstat** bool: Collect per-operation type metrics
 
 #### Description
 
 The NFSCLIENT plugin collects data from /proc/self/mountstats, by default it will only include a quite limited set of IO metrics. 
 If fullstat is set, it will collect a lot of per-operation statistics.
 
+#### Measurements & Fields
+
+- nfsstat_read
+    - read_bytes (integer, bytes)
+    - read_exe (integer, bytes)
+    - read_ops (integer, bytes)
+    - read_retrans (integer, miliseconds)
+    - read_rtt (integer, miliseconds)
+
+- nfsstat_write
+    - write_bytes (integer, bytes)
+    - write_ops (integer, bytes)
+    - write_retrans (integer, bytes)
+    - write_exe (integer, miliseconds)
+    - write_rtt (integer, miliseconds)
+
+In addition enabling fullstat will make many more metrics available.
+
+#### Tags
+
+- All measurements have the following tags:
+    - mountpoint The local mountpoint, for instance: "/var/www"
+    - serverexport The full server export, for instance: "nfsserver.example.org:/export"
+
 #### References
 [nfsiostat](http://git.linux-nfs.org/?p=steved/nfs-utils.git;a=summary)
+[net/sunrpc/stats.c - Linux source code](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/sunrpc/stats.c)
 
 [What is in /proc/self/mountstats for NFS mounts: an introduction](https://utcc.utoronto.ca/~cks/space/blog/linux/NFSMountstatsIndex)