Update obtaining-login-credentials.md

docs.it4i/general/obtaining-login-credentials/obtaining-login-credentials.md

@@ -8,7 +8,7 @@ If you are not eligible for an e-INFRA CZ account, contact the [IT4I support][a]
 1. Full name, country/countries of citizenship, academic affiliation, and country of affiliation
 1. Statement that you have read and accepted the [Acceptable use policy document][c] (AUP)
 1. Attach the AUP file
-1. Your preferred username (length is limited between 4 and 7 letters)<br>The preferred username must associate with your first and last name or be otherwise derived from it. Only alphanumeric sequences and dash signs are allowed. Note that the system will automatically add the `it4i-` prefix to your username.
+1. Your preferred username (length is limited between 4 and 7 letters)<br>The preferred username must associate with your first and last name or be otherwise derived from it. Note that the system will automatically add the `it4i-` prefix to your username.
 1. Public part of your SSH key<br>If you don't provide it in the ticket, you must [add it manually][s] after your account is created.
 1. All information above should be provided by email, the email must be digitally signed by a CA authority. Read more on [digital signatures][4] below. If you do not have such a digital signature, you can choose an [Alternative way to personal certificate][3]; a scan of photo ID (personal ID or passport or driver license) is required.