readme: the version is a subcommand, not a flag

The flags table advertised -v/--version; neither exists — cobra prints
usage for both. `sdns version` is the real spelling, and it reports the
Go toolchain alongside the version.

Author: semihalev

README.md

@@ -99,9 +99,10 @@ $ make test
 | ----------------- | ------------------------------------------------------------------------------ |
 | -c, --config PATH | Location of the config file. If it doesn't exist, a new one is generated at that path. Default: sdns.conf (working directory) |
 | -t, --test        | Test configuration file and exit. Returns exit code 0 if valid, 1 if invalid. Checks every setting it can judge — addresses, IPs, CIDRs, enumerated values, upstream formats, TLS files — and reports all problems at once. It also fails on keys the file carries that no setting claims: a typo, or a key an older SDNS understood. Startup only warns about those, so upgrading with a stale key does not become an outage |
-| -v, --version     | Show the SDNS version                                                          |
 | -h, --help        | Show help information and exit                                                 |
 
+`sdns version` prints the SDNS version and the Go toolchain it was built with.
+
 ## Debugging Environment
 
 To debug your environment, execute the following command: