Merge pull request #152 from daliboris/fix/add-ngram-index-name

fix(documentation): add ngram-index to the list of indexes

Author: joewiz

src/main/xar-resources/data/docs/util/index-keys_5.md

@@ -46,10 +46,11 @@ had been defined (otherwise nothing will be returned).
 
 # Index names
 
-The default names for indexes are as follows:
+The default names for indexes are as follows (some of them can be found in the eXist-db `conf.xml` file under `exist/indexer/modules` element):
 
 Name|Index
 ----|-----
 structural-index|Structural index
 lucene-index|Lucene-based full text index
-range-index|New range index
+range-index|New range index
+ngram-index|N-gram index