add custom analyzer link

Author: jrodewig

docs/reference/analysis/tokenfilters/apostrophe-tokenfilter.asciidoc

@@ -70,7 +70,7 @@ The filter produces the following tokens:
 ==== Add to an analyzer
 
 The following <<indices-create-index,create index API>> request adds the
-apostrophe token filter to an analyzer.
+apostrophe token filter to a <<analysis-custom-analyzer,custom analyzer>>.
 
 [source,console]
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