SQL server Read Only permission automatically for new databases
Reference:
model Database


  The model database is used as the template for all databases created
  on an instance of SQL Server. Because tempdb is created every time SQL
  Server is started, the model database must always exist on a SQL
  Server system. The entire contents of the model database, including
  database options, are copied to the new database. Some of the settings
  of model are also used for creating a new tempdb during start up, so
  the model database must always exist on a SQL Server system.


Add the user to your model database db_datareader role.  All future database will mimic this privilege. 

USE [model]
GO
CREATE USER [sqllogin1] FOR LOGIN [sqllogin1]
GO
USE [model]
GO
ALTER ROLE [db_datareader] ADD MEMBER [sqllogin1]
GO


Once you run this sqllogin1 user will be created in all new database and will be a member of db_datareader role.