doc: make README formatting more consistent

In order to be consistent with the previous items,
I split the sentence.

PR-URL: nodejs#25003
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

README.md

@@ -52,8 +52,8 @@ resources:
 * [Questions tagged 'node.js' on StackOverflow][]
 * [#node.js channel on chat.freenode.net][]
 * [Node.js Discord Community](https://discordapp.com/invite/v7rrPdE)
-* [Node.js Slack Community](https://node-js.slack.com/): Visit
-  [nodeslackers.com](http://www.nodeslackers.com/) to register.
+* [Node.js Slack Community](https://node-js.slack.com/)
+  * To register: [nodeslackers.com](http://www.nodeslackers.com/)
 
 GitHub issues are for tracking enhancements and bugs, not general support.