Update explanation about existing plugins

README.md

@@ -1,8 +1,24 @@
 # fluent-plugin-filter-split
 
-[Fluentd](https://fluentd.org/) filter plugin to do something.
-
-TODO: write description for you plugin.
+[Fluentd](https://fluentd.org/) filter plugin to split specified field.
+
+Compared to existing plugins:
+
+* https://github.com/wshihadeh/fluent-plugin-record-splitter
+  * This is filter plugin. It splits the specified field into multiple records. The target field must be lines.
+* https://github.com/unquietwiki/fluent-plugin-split_record
+  * This is filter plugin. It splits the specified field into key/value pairs. The target field must contain "key=value" pairs.
+* https://github.com/SNakano/fluent-plugin-split-array
+  * This is filter plugin. It splits the specified field into multiple records. The target field must be always array.
+* https://github.com/toyama0919/fluent-plugin-split
+  * This is output plugin. It splits the specified field into multiple records. The target field must contains specific separator.
+* https://github.com/activeshadow/fluent-plugin-split-event
+  * This is filter plugin. It splits the specified field into multiple records. The target field must contains specific separator.
+* https://github.com/bitpatty/fluent-plugin-filter-split-message
+  * 404. The only gem exists. https://rubygems.org/gems/fluent-plugin-filter-split-message
+  * This is filter plugin. It splits the specified field into multiple records. The target field must contains specific separator.
+
+Thus, about above plugins, there are limitation of type of field or missing feature to control keep/remove other fields.
 
 ## Installation
 
@@ -28,13 +44,12 @@ $ bundle
 
 ## Configuration
 
-You can generate configuration template:
-
-```
-$ fluent-plugin-config-format filter filter-split
-```
-
-You can copy and paste generated documents here.
+|parameter|type|description|default|
+|---|---|---|---|
+|split_key|string (required)|Specify a target key to split||
+|keep_other_key|bool (optional)|Specify a flag whether other key must be kept or not||
+|keep_keys|array (optional)|Specify keys to be kept in filtered record|`[]`|
+|remove_keys|array (optional)|Specify keys to be removed in filtered record|`[]`|
 
 ## Copyright