doc: use sentence case in README.md headers

PR-URL: #37645
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

Author: marsonya

README.md

@@ -21,19 +21,19 @@ The Node.js project uses an [open governance model](./GOVERNANCE.md). The
 # Table of contents
 
 *[Support](#support)
-*[Release Types](#release-types)
+*[Release types](#release-types)
 *[Download](#download)
-*[Current and LTS Releases](#current-and-lts-releases)
-*[Nightly Releases](#nightly-releases)
-*[API Documentation](#api-documentation)
-*[Verifying Binaries](#verifying-binaries)
+*[Current and LTS releases](#current-and-lts-releases)
+*[Nightly releases](#nightly-releases)
+*[API documentation](#api-documentation)
+*[Verifying binaries](#verifying-binaries)
 *[Building Node.js](#building-nodejs)
 *[Security](#security)
 *[Contributing to Node.js](#contributing-to-nodejs)
-*[Current Project Team Members](#current-project-team-members)
+*[Current project team members](#current-project-team-members)
 *[TSC (Technical Steering Committee)](#tsc-technical-steering-committee)
 *[Collaborators](#collaborators)
-*[Release Keys](#release-keys)
+*[Release keys](#release-keys)
 *[License](#license)
 
 ## Support