Create README.md (#1)

Author: ChuckHend

README.md

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+# pg_later
+Execute SQL now and get the results later.
+
+A postgres extension to execute queries asynchronously. 
+
+```sql
+CREATE EXTENSION pg_later CASCADE
+```
+
+Execute a SQL query now:
+
+```sql
+select pg_later_exec(
+  'select * from pg_available_extensions order by name limit 2'
+) as job_id
+
+ job_id 
+--------
+     1
+(1 row)
+```
+
+Come back at some later time, and retrieve the results by providing the job id:
+
+```sql
+select pg_later_results(1)
+
+ pg_later_results                                                                                                                                                                                       
+--------------------
+{
+  "query": "select * from pg_available_extensions order by name limit 2",
+  "job_id": 48,
+  "result": [
+    {
+      "name": "adminpack",
+      "comment": "administrative functions for PostgreSQL",
+      "default_version": "2.1",
+      "installed_version": null
+    },
+    {
+      "name": "amcheck",
+      "comment": "functions for verifying relation integrity",
+      "default_version": "1.3",
+      "installed_version": null
+    }
+  ],
+  "status": "success"
+}
+```