fix: a service account may be named by a GUID in lowercase, as the Router Manager proposes for a new one.

README.md

@@ -717,7 +717,9 @@ vpn-router-user otp-remove alice
 | `console <name> (--posix \| --account LOCAL \| --off)` | Switches the console login of a member of `admins` enrolled for TOTP on, as the user's own POSIX account or a local account, or off (see Console login and SSH) |
 | `passkeys-remove <name>` | Removes all the user's passkeys (see Passkeys) |
 
-A user name is 1 to 32 lowercase letters, digits and hyphens, starting with a letter; a
+A user name is 1 to 32 lowercase letters, digits and hyphens, starting with a letter, and a
+service account may instead be named by a GUID in lowercase, such as
+`3f2b8c1e-9a4d-4e6f-8b2a-1c5d7e9f0a3b`; a
 password has 8 to 128 characters; a first or last name has 1 to 64 printable characters; an
 e-mail address has one `@`, no spaces and a dot in its domain; a TOTP secret is 32 base32
 characters, as `otp-new` makes it, and a code 6 digits. Once enrolled, a user logs in to OpenVPN