Update documented groupnames scheme to use varchar instead of text.

Avoids:
ERROR 1170 (42000): BLOB/TEXT column 'uid' used in key specification without a key length

modules/sqlauth/docs/sql.txt

@@ -41,8 +41,8 @@ Database layout used in some of the examples:
       eduPersonPrincipalName TEXT NOT NULL
     );
     CREATE TABLE usergroups (
-      uid TEXT REFERENCES users (uid) ON DELETE CASCADE ON UPDATE CASCADE,
-      groupname TEXT,
+      uid VARCHAR(30) NOT NULL REFERENCES users (uid) ON DELETE CASCADE ON UPDATE CASCADE,
+      groupname VARCHAR(30) NOT NULL,
       UNIQUE(uid, groupname)
     );