Declarative partitioning with Postgres for integer column
It should be done manually.  From the doc page (already mentioned in the question) 
 - https://www.postgresql.org/docs/10/static/ddl-partitioning.html#DDL-PARTITIONING-DECLARATIVE) -
under 


  5.10.2.1 Example  To use declarative partitioning in this case, use the following steps: ....  
  
  
  Create partitions. Each partition's definition must specify the bounds that correspond to the partitioning method and partition key of
  the parent. Note that specifying bounds such that the new partition's
  values will overlap with those in one or more existing partitions will
  cause an error. Inserting data into the parent table that does not map
  to one of the existing partitions will cause an error; an appropriate
  partition must be added manually."