Update the README with some details related to Go version used by the…

… rules

Signed-off-by: Cosmin Cojocar <cosmin@cojocar.ch>

README.md

@@ -230,6 +230,12 @@ You can also configure the hard-coded credentials rule `G101` with additional pa
 }
 ```
 
+#### Go version
+
+Some rules require a specific Go version which is retrieved from the Go module file present in the project. If this version cannot be found, it will fallback to Go runtime version.
+
+The Go module version is parsed using the `go list` command which in some cases might lead to performance degradation. In this situation, the go module version can be easily disabled by setting the environment variable `GOSECNOMODVERSION=on`.
+
 ### Dependencies
 
 gosec will fetch automatically the dependencies of the code which is being analyzed when go module is turned on (e.g.`GO111MODULE=on`). If this is not the case,