Create README.md

Add project description, a list of all functions which will be added in the first batch and a guide on how to create these functions in your database.

Author: derk-vanveen

README.md

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+# adyen-postgres-partitioning
+These functions are designed to create and maintain partitions in PostgreSQL with a minimal impact on the applicaton. The priority is to not impact the application. When possible, the weakest lock possible is being used, when a heavy lock is required we use a timeout to prevent long lasting locks. 
+
+Every function in this project starts with a detailed comment on what function does and how to use it. 
+
+# Features
+The functions in this project can
+
+- Partition an existing table. The origional table will not partitioned itself, but becomes the first partition
+- Add indexes to a partitioned table and all children
+- Add foreign keys to a partitioned table and all children
+- Add date constraints to a table partitioned on an integer column
+- Count the number of available, unused partitions
+- Get the details for the last partition
+- Add new partitions to a partitioned table. The new partitions will have the same properties as the latest available partition
+- Detach partitions from a partitioned table
+- Drop detached partitions
+
+# Installation
+You can add the individual functions directly on the database from `psql` with the `\i` command. Use `psql` to login on your database and run
+```sql
+\i <full path to the function>.<filename>.sql
+```
+N.B. Some functions use other functions.