Docs: fixed ICU plugin documentation

add ICU Normalization CharFilter to docs

Closes #6711

docs/reference/analysis/icu-plugin.asciidoc

@@ -218,3 +218,29 @@ Breaks text into words according to UAX #29: Unicode Text Segmentation ((http://
 }
 --------------------------------------------------
 
+
+[float]
+=== ICU Normalization CharFilter
+
+Normalizes characters as explained http://userguide.icu-project.org/transforms/normalization[here].
+It registers itself by default under `icu_normalizer` or `icuNormalizer` using the default settings.
+Allows for the name parameter to be provided which can include the following values: `nfc`, `nfkc`, and `nfkc_cf`.
+Allows for the mode parameter to be provided which can include the following values: `compose` and `decompose`.
+Use `decompose` with `nfc` or `nfkc`, to get `nfd` or `nfkd`, respectively.
+Here is a sample settings:
+
+[source,js]
+--------------------------------------------------
+{
+    "index" : {
+        "analysis" : {
+            "analyzer" : {
+                "collation" : {
+                    "tokenizer" : "keyword",
+                    "char_filter" : ["icu_normalizer"]
+                }
+            }
+        }
+    }
+}
+--------------------------------------------------