Update README.md

README.md

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 # mono-cli
-CLI tool that exports mono statements to csv
+CLI tool that exports mono statements in csv format and prints it to stdout.
+Works only with personal API key.
+
+### Limitations
+Due to monobank API limitations tool can only load statements for 31 days period in one request and only send one request per 60 seconds. So if you launched a tool and it's still running and nothing printed - just wait. 
+
+### Configuration
+Tool can be configured using following environment variables
+```
+MONO_APIKEY - required. Your personal API key, see https://api.monobank.ua/
+
+MONO_STARTDATE - this tool will import statements occured after this date. Expected format: unix timestamp in UTC. If not set default value is monobank launch date (15 Nov 2017)
+
+MONO_STARTDATE - this tool will import statements occured before this date. Expected format: unix timestamp in UTC. If not set default value is current date time
+```