Update README for pgbouncer config

Add a note in the documentation that the pgbouncer.ini may need to be
updated.

Fixes: #99

Signed-off-by: SuperQ <[email protected]>

Author: SuperQ

Diff for: README.md

@@ -13,6 +13,11 @@ To see all available configuration flags:
 
     ./pgbouncer_exporter -h
 
+## PGBouncer configuration
+
+The pgbouncer\_exporter requires a configuration change to pgbouncer to ignore a PostgreSQL driver connection parameter. In the `pgbouncer.ini` please include this option:
+
+    ignore_startup_parameters = extra_float_digits
 
 ## Metrics