doc: update maintaining-V8.md

Updated to conform to style guide.

PR-URL: #31503
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: kzs0

doc/guides/maintaining-V8.md

@@ -30,7 +30,7 @@ For example, at the time of this writing:
 
 All older branches are abandoned and are not maintained by the V8 team.
 
-### V8 merge process overview
+### V8 Merge Process Overview
 
 The process for backporting bug fixes to active branches is officially
 documented [on the V8 wiki][V8MergingPatching]. The summary of the process is:
@@ -278,7 +278,7 @@ PR-URL: https://github.com/nodejs/node/pull/7833
   normal and [V8 CI][] using the Node.js CI system. We only needed to backport
   to `v6.x` as the other LTS branches weren't affected by this bug.
 
-### Backports Identified by the V8 team
+### Backports Identified by the V8 Team
 
 For bugs found through the browser or other channels, the V8 team marks bugs
 that might be applicable to the abandoned branches in use by Node.js. This is
@@ -317,7 +317,7 @@ V8 builds against the version of ICU supplied by Node.js,
 see [maintaining-icu.md](./maintaining-icu.md) for special considerations.
 Specifically, a V8 update may necessitate an ICU update.
 
-### Minor updates (patch level)
+### Minor Updates (Patch Level)
 
 Because there may be floating patches on the version of V8 in Node.js, it is
 safest to apply the patch level updates as a patch. For example, imagine that
@@ -382,7 +382,7 @@ git node v8 major --branch=5.1-lkgr
 
 This should be followed up with manual refloating of all relevant patches.
 
-## Proposal: Using a fork repo to track upstream V8
+## Proposal: Using a Fork Repo to Track Upstream V8
 
 The fact that Node.js keeps a vendored, potentially edited copy of V8 in deps/
 makes the above processes a bit complicated. An alternative proposal would be to