README.md in sensu-plugins-postgres-1.3.0 vs README.md in sensu-plugins-postgres-1.4.0

@@ -23,10 +23,87 @@
  * bin/check-postgres-query.rb
  * bin/metrics-postgres-query.rb
 
 ## Usage
 
+Use `--help` to see command arguments.
+
+### Sample usage
+
+#### Check if PostgreSQL is alive
+```
+$ check-postgres-alive.rb -d template1 -f /var/lib/postgresql/.pgpass
+CheckPostgres OK: Server version: {"version"=>"PostgreSQL 9.6.3 on x86_64-pc-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit"}
+```
+
+### Check replication status
+```
+$ check-postgres-replication.rb -m psql1.local -s psql2.local -d template1 -w 5 -c 10
+CheckPostgresReplicationStatus OK: replication delayed by 0.0MB :: master:B0/B4031000 slave:B0/B4031000 m_segbytes:16777216
+```
+
+### Check number of connections
+```
+$ export PGPASSWORD=this-is-secret-password
+$ check-postgres-connections.rb -a -w 80 -c 90 -d template1 -u sensu
+CheckPostgresConnections OK: PostgreSQL connections under threshold: 17%, 174 out of 997 connections
+```
+
+### Default values
+
+| Argument       | Env variable | Value     |
+|----------------|--------------|-----------|
+| -f, --pgpass   | PGPASSFILE   | ~/.pgpass |
+| -h, --hostname | PGHOST       | localhost |
+| -P, --port     | PGPORT       | 5432      |
+| -d, --database | PGDATABASE   | postgres  |
+| -u, --user     | PGUSER       | postgres  |
+| -p, --password | PGPASSWORD   |           |
+
+Options precedence is following:
+1. command line arguments
+1. pgpass file
+1. env variables
+1. defaults
+
+### Pgpass file
+
+When file `~/.pgpass` is found it is used by default. You can also use `-f, --pgpass` command line argument or set `PGPASSFILE` env variable.
+
+File format is:
+
+```
+hostname:port:database:username:password
+```
+
+Only first line is used. If database is set to `*` it is ommited.
+
+You can ovveride `pgpass` values with command line arguments, e.g. `-h` for hostname.
+
 ## Installation
 
-[Installation and Setup](http://sensu-plugins.io/docs/installation_instructions.html)
+```
+gem install sensu-plugins-postgres
+```
+
+See [Installation and Setup](http://sensu-plugins.io/docs/installation_instructions.html) for details.
+
+### Known issues
+
+When using Sensu with `EMBEDDED_RUBY=true` and installing Postgres checks with `/usr/bin/sensu-install -p sensu-plugins-postgres` you might get following error:
+
+```
+ERROR:  Error installing sensu-plugins-postgres:
+	ERROR: Failed to build gem native extension.
+[...]
+checking for PQconnectdb() in -lpq... no
+checking for PQconnectdb() in -llibpq... no
+checking for PQconnectdb() in -lms/libpq... no
+Can't find the PostgreSQL client library (libpq)
+*** extconf.rb failed ***
+```
+
+The reason is that **libssl** library which comes with Sensu is incompatible with **libpq** library installed on your system. There is no easy way to fix it. You might want to install sensu-plugins-postgres globally with `gem install sensu-plugins-postgres`.
+
+Checks are in `/usr/local/bin` directory.
 
 ## Notes