mongodb_plugin: python README update

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diff --git a/python.d/README.md b/python.d/README.md
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--- a/python.d/README.md
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@@ -710,6 +710,149 @@ If no configuration is given, module will attempt to connect to memcached instan
 
 ---
 
+# mongodb
+
+Module monitor mongodb performance and health metrics
+
+**Requirements:**
+ * `python-pymongo` package.
+
+You need to install it manually.
+
+
+Number of charts depends on mongodb version, storage engine and other features (replication):
+
+1. **Read requests**:
+ * query
+ * getmore (operation the cursor executes to get additional data from query)
+
+2. **Write requests**:
+ * insert
+ * delete
+ * update
+
+3. **Active clients**:
+ * readers (number of clients with read operations in progress or queued)
+ * writers (number of clients with write operations in progress or queued)
+
+4. **Journal transactions**:
+ * commits (count of transactions that have been written to the journal)
+
+5. **Data written to the journal**:
+ * volume (volume of data)
+
+6. **Background flush** (MMAPv1):
+ * average ms (average time taken by flushes to execute)
+ * last ms (time taken by the last flush)
+
+8. **Read tickets** (WiredTiger):
+ * in use (number of read tickets in use)
+ * available (number of available read tickets remaining)
+
+9. **Write tickets** (WiredTiger):
+ * in use (number of write tickets in use)
+ * available (number of available write tickets remaining)
+
+10. **Cursors**:
+ * opened (number of cursors currently opened by MongoDB for clients)
+ * timedOut (number of cursors that have timed)
+ * noTimeout (number of open cursors with timeout disabled)
+
+11. **Connections**:
+ * connected (number of clients currently connected to the database server)
+ * unused (number of unused connections available for new clients)
+
+12. **Memory usage metrics**:
+ * virtual
+ * resident (amount of memory used by the database process)
+ * mapped
+ * non mapped
+
+13. **Page faults**:
+ * page faults (number of times MongoDB had to request from disk)
+
+14. **Cache metrics** (WiredTiger):
+ * percentage of bytes currently in the cache (amount of space taken by cached data)
+ * percantage of tracked dirty bytes in the cache (amount of space taken by dirty data)
+
+15. **Pages evicted from cache** (WiredTiger):
+ * modified
+ * unmodified
+
+16. **Queued requests**:
+ * readers (number of read request currently queued)
+ * writers (number of write request currently queued)
+
+17. **Errors**:
+ * msg (number of message assertions raised)
+ * warning (number of warning assertions raised)
+ * regular (number of regular assertions raised)
+ * user (number of assertions corresponding to errors generated by users)
+
+18. **Storage metrics** (one chart for every database)
+ * dataSize (size of all documents + padding in the database)
+ * indexSize (size of all indexes in the database)
+ * storageSize (size of all extents in the database)
+
+19. **Documents in the database** (one chart for all databases)
+ * documents (number of objects in the database among all the collections)
+
+20. **tcmalloc metrics**
+ * central cache free
+ * current total thread cache
+ * pageheap free
+ * pageheap unmapped
+ * thread cache free
+ * transfer cache free
+ * heap size
+
+21. **Commands total/failed rate**
+ * count
+ * createIndex
+ * delete
+ * eval
+ * findAndModify
+ * insert
+
+22. **Locks metrics** (acquireCount metrics - number of times the lock was acquired in the specified mode)
+ * Global lock
+ * Database lock
+ * Collection lock
+ * Metadata lock
+ * oplog lock
+
+23. **Replica set members state**
+ * state
+
+24. **Oplog window**
+  * window (interval of time between the oldest and the latest entries in the oplog)
+
+25. **Replication lag**
+  * member (time when last entry from the oplog was applied for every member)
+
+26. **Replication set member heartbeat latency**
+  * member (time when last heartbeat was received from replica set member)
+
+
+### configuration
+
+Sample:
+
+```yaml
+local:
+    name : 'local'
+    host : '127.0.0.1'
+    port : 27017
+    user : 'netdata'
+    pass : 'netdata'
+
+```
+
+If no configuration is given, module will attempt to connect to mongodb daemon on `127.0.0.1:27017` address
+
+---
+
+
 # mysql
 
 Module monitors one or more mysql servers