docs: clarify legacy token creation in npm login and adduser commands

Author: LiangYingC

docs/lib/content/commands/npm-adduser.md

@@ -14,6 +14,8 @@ Create a new user in the specified registry, and save the credentials to
 the `.npmrc` file. If no registry is specified, the default registry
 will be used (see [`registry`](/using-npm/registry)).
 
+When you run `npm adduser`, the CLI automatically generates a legacy token of publish type. For more information, see [About legacy tokens](/about-access-tokens#about-legacy-tokens).
+
 When using `legacy` for your `auth-type`, the username, password, and
 email are read in from prompts.
 

docs/lib/content/commands/npm-login.md

@@ -14,6 +14,8 @@ Verify a user in the specified registry, and save the credentials to the
 `.npmrc` file. If no registry is specified, the default registry will be
 used (see [`config`](/using-npm/config)).
 
+When you run `npm login`, the CLI automatically generates a legacy token of publish type. For more information, see [About legacy tokens](/about-access-tokens#about-legacy-tokens).
+
 When using `legacy` for your `auth-type`, the username and password, are
 read in from prompts.