DOCSP-13850 indexes (#112)

* added indexes page

Author: kyuan-mongodb

source/fundamentals.txt

@@ -15,13 +15,13 @@ Fundamentals
    /fundamentals/bson
    /fundamentals/crud
    /fundamentals/aggregation
+   /fundamentals/indexes
    /fundamentals/time-series
 
 ..
   /fundamentals/enterprise-auth
   /fundamentals/databases-collections
   /fundamentals/data-formats
-  /fundamentals/indexes
   /fundamentals/builders
   /fundamentals/collations
   /fundamentals/csfle