Improve Keyset::Sequel and docs

docs/api/keyset.md

@@ -94,6 +94,12 @@ performance). You do it once during development, and pagy will be fast at each r
   `next`,... : it's exactly the same as going backward like: `last`, `prev`, `prev`, ... 
 !!!
 
+## How pagy keyset works
+
+You pass an uniquely ordered `set`, and `Pagy::Keyset` queries the page of records, keeping track of the last retrieved record by 
+encoding it into the `page` param of the `next` URL. At each request the `:page` is decoded and used to prepare a `when` clause 
+that excludes the records retrived up to that point and pulls the `:limit` of requested records.
+
 ### ORMs
 
 `Pagy::Keyset` implements the subclasses for `ActiveRecord::Relation` and `Sequel::Dataset` sets and instantiate them internally:
@@ -106,12 +112,6 @@ Pagy::Keyset.new(sequel_set)
 #=> #<Pagy::Keyset::Sequel:0x00000001066545e0>
 ```
 
-## How pagy keyset works
-
-You pass an uniquely ordered `set`, and `Pagy::Keyset` queries the page of records, keeping track of the last retrieved record by 
-encoding it into the `page` param of the `next` URL. At each request the `:page` is decoded and used to prepare a `when` clause 
-that excludes the records retrived up to that point and pulls the `:limit` of requested records.
-
 ## Variables
 
 === `:page`