diff --git a/README.md b/README.md
index 9d13201..6ef3fae 100644
--- a/README.md
+++ b/README.md
@@ -5,25 +5,65 @@ is a simple node process that will follow a couchdb changes feed and updates ela
 
 You can also include an optional mapper.
 
-```
+```sh
 npm install couch2elastic4sync -g
 ```
 
 ## Usage
 
+### Configuration file
+
 [rc](http://npm.im/rc) is used to set to variables. For example, create a .couch2elastic4sync file with the following
+```ini
+database=http://localhost:5984/idx-edm-v5
+elasticsearch=http://elastic-1.com:9200/idx-edm-v5/listing
+```
+
+or pass the config file path explicity
+```ini
+couch2elastic4sync --config=path/to/configfile
+```
+
+Alternatively, the config file can be in JSON
+```json
+{
+  "database": "http://localhost:5984/idx-edm-v5",
+  "elasticsearch": "http://elastic-1.com:9200/idx-edm-v5/listing"
+}
+```
 
-    database=http://localhost:5984/idx-edm-v5
-    elasticsearch=http://elastic-1.com:9200/idx-edm-v5/listing
+### Load documents
 
 To load all the documents into elasticsearch, run
+```sh
+couch2elastic4sync load
+```
 
-    couch2elastic4sync load
+### Keep documents in sync
 
 To keep a sync process going, run
+```sh
+couch2elastic4sync
+```
 
-    couch2elastic4sync
+### Format and filter documents
+
+A `mapper` function can be passed from the config to format documents before being put to ElasticSearch:
+```ini
+database=http://localhost:5984/idx-edm-v5
+elasticsearch=http://elastic-1.com:9200/idx-edm-v5/listing
+mapper=path/to/my-mapper.js
+```
+
+Where my-mapper.js could be something like
+```
+module.exports = function (doc) {
+  // apply formatting here
+  return doc
+}
+```
 
+If the function returns empty, the document is filtered-out
 
 ## License
 
diff --git a/lib/load.js b/lib/load.js
index 12e3b11..cd477d7 100644
--- a/lib/load.js
+++ b/lib/load.js
@@ -22,7 +22,9 @@ module.exports = function (config, log, done) {
       var result = row.doc
       if (config.mapper) {
         result = config.mapper(row.doc)
-        if (result && config.addRaw) result[config.rawField] = row.doc
+        // return if the document was filtered-out
+        if (!result) return cb()
+        if (config.addRaw) result[config.rawField] = row.doc
         result._id = row.id // we need this to work correct
       }
       cb(null, result)