add documentation to view docker logs

README.md

@@ -27,3 +27,22 @@ The Joystream Storage-Squid is a [Subsquid](https://docs.subsquid.io/) based pro
 make prepare # install dependencies and build the project
 make up-squid # start the storage-squid processor and the GraphQL server
 ```
+
+## Logging 
+
+The storage-squid uses the `@subsquid/logger` package for logging. The logger is configured to log to `stderr` and the log level is determined by the `SQD_*` environment variables. 
+
+By default, the log level for Storage Squid processor is set to `SQD_DEBUG=sqd:processor:mapping`. This means that all loggers will log at `DEBUG` level. So the processor logs will contain `DEBUG`, `INFO`, `WARN`, `ERROR` and `FATAL` logs (The integer values for these logging levels are `1`, `2`, `3`, `4` and `5` respectively).
+
+However, sometimes it is very difficult to analyze the processor logs because of the high volume of DEBUG logs. So maybe you only want to see `INFO`, `WARN`, `ERROR` and `FATAL` logs. You can do this by using the `docker logs ...` command in the following way
+
+```bash
+# Only INFO logs
+docker logs squid_processor 2>&1 | grep -E "\"level\":2" 
+
+# INFO and above logs
+docker logs squid_processor -f 2>&1 | grep -E "\"level\":2|\"level\":3|\"level\":4|\"level\":5" 
+
+# You can also use other docker logs options like --follow, --tail etc
+docker logs squid_processor --follow --tail 100 2>&1 | grep -E "\"level\":2|\"level\":3|\"level\":4|\"level\":5" 
+```