Fix link to node in readme (#1255)

* Fix link to node in readme

Link to node points to nothing in readme, changed the link.
Also made the table of content name consistent with the section title and made npm lowercase as it should.

* More NPM occurences

README.md

@@ -22,7 +22,7 @@
   <span>&nbsp;&nbsp;•&nbsp;&nbsp;</span>
   <a href="https://discord.gg/RcG33DQJdf">Discord</a>
   <span>&nbsp;&nbsp;•&nbsp;&nbsp;</span>
-  <a href="https://www.npmjs.com/package/zod">NPM</a>
+  <a href="https://www.npmjs.com/package/zod">npm</a>
   <span>&nbsp;&nbsp;•&nbsp;&nbsp;</span>
   <a href="https://github.com/colinhacks/zod/issues/new">Issues</a>
   <span>&nbsp;&nbsp;•&nbsp;&nbsp;</span>
@@ -47,7 +47,7 @@
   - [Sponsors](#sponsors)
   - [Ecosystem](#ecosystem)
 - [Installation](#installation)
-  - [Node](#node)
+  - [Node/npm](#Node/npm)
   - [Deno](#deno)
 - [Basic usage](#basic-usage)
 - [Primitives](#primitives)
@@ -338,7 +338,7 @@ There are a growing number of tools that are built atop or support Zod natively!
   }
   ```
 
-### Node/NPM
+### Node/npm
 
 To install Zod v3:
 
@@ -350,7 +350,7 @@ pnpm add zod          # pnpm
 
 ### Deno
 
-Unlike Node, Deno relies on direct URL imports instead of a package manager like NPM. Zod is available on [deno.land/x](deno.land/x). The latest version can be imported like so:
+Unlike Node, Deno relies on direct URL imports instead of a package manager like npm. Zod is available on [deno.land/x](deno.land/x). The latest version can be imported like so:
 
 ```ts
 import { z } from "https://deno.land/x/zod/mod.ts";
@@ -362,7 +362,7 @@ You can also specify a particular version:
 import { z } from from "https://deno.land/x/zod@v3.16.1/mod.ts"
 ```
 
-> The rest of this README assumes you are using NPM and importing directly from the `"zod"` package.
+> The rest of this README assumes you are using npm and importing directly from the `"zod"` package.
 
 ## Basic usage