npm-login: add page (#14768)

pages/common/npm-login.md

@@ -0,0 +1,16 @@
+# npm login
+
+> Login to a registry user account.
+> More information: <https://docs.npmjs.com/cli/commands/npm-login>.
+
+- Login to a registry user account and save the credentials to the `.npmrc` file:
+
+`npm login`
+
+- Login, using a custom registry:
+
+`npm login --registry={{registry_url}}`
+
+- Login, using a specific authentication strategy:
+
+`npm login --auth-type={{legacy|web}}`