Add README

Co-authored-by: prabhu43 <j.prabhu91@gmail.com>

Author: aswinkarthik

README.md

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+# pg-ping
+
+`pg-ping` is a command line utility to continously ping your postgres. This is useful to check if there is downtime when doing changes to your postgres instance.
+
+## Configuration
+
+```bash
+export PGPING_USERNAME=your-username
+export PGPING_PASSWORD=your-password
+export PGPING_HOST=your-host
+export PGPING_DBNAME=your-dbname
+export PGPING_QUERY=your-query # default is select 1
+export PGPING_FREQUENCYINMS=300 # default is 1 second
+```
+
+## Usage
+
+```bash
+$ pg-ping
+{"Value":"1","TimeTakenInMS":0.408563,"Failed":false,"FailureMessage":""}
+{"Value":"1","TimeTakenInMS":0.46392500000000003,"Failed":false,"FailureMessage":""}
+{"Value":"","TimeTakenInMS":0.634099,"Failed":true,"FailureMessage":"dial tcp 10.134.125.111:5432: connect: connection refused"} # Downtime
+{"Value":"","TimeTakenInMS":0.402107,"Failed":true,"FailureMessage":"dial tcp 10.134.125.111:5432: connect: connection refused"}
+{"Value":"1","TimeTakenInMS":10.726904000000001,"Failed":false,"FailureMessage":""}
+{"Value":"1","TimeTakenInMS":0.372709,"Failed":false,"FailureMessage":""}
+{"Value":"1","TimeTakenInMS":0.429533,"Failed":false,"FailureMessage":""}
+```
+
+## Build
+
+```
+go build -o pg-ping main.go
+```