doc: document the git command

Author: joyeecheung

README.md

@@ -13,6 +13,9 @@ CLI tools for Node.js Core collaborators.
   - [Install](#install)
   - [Setting up credentials](#setting-up-credentials)
 - [`ncu-config`](#ncu-config)
+- [`git-node`](#git-node)
+  - [Prerequistes](#prerequistes)
+  - [Demo & Usage](#demo--usage)
 - [`get-metadata`](#get-metadata)
   - [Git bash for Windows](#git-bash-for-windows)
   - [Features](#features)
@@ -85,6 +88,48 @@ Options:
   --global                                            [boolean] [default: false]
 ```
 
+## `git-node`
+
+A custom Git command for landing pull requests. You can run it as
+`git-node` or `git node`. To see the help text, run `git node help`.
+
+### Prerequistes
+
+1. It's a Git command, so make sure you have Git installed, of course.
+2. Install [core-validate-commit](https://github.com/nodejs/core-validate-commit)
+
+    ```
+    $ npm install -g core-validate-commit
+    ```
+3. Configure your upstream remote and branch name. By default it assumes your
+  remote pointing to https://github.com/nodejs/node is called `upstream`, and
+  the branch that you are trying to land PRs on is `master`. If that's not the
+  case:
+
+    ```
+    $ cd path/to/node/project
+    $ ncu-config upstream your-remote-name
+    $ ncu-config branch your-branch-name 
+    ```
+
+### Demo & Usage
+
+1. Landing multiple commits: https://asciinema.org/a/148627
+2. Landing one commit: https://asciinema.org/a/157445
+
+```
+$ cd path/to/node/project
+$ git node land --abort          # Abort a landing session, just in case
+$ git node land $PRID            # Start a new landing session
+
+$ git rebase -i upstream/master  # Put `edit` on every commit that's gonna stay
+
+$ git node land --amend          # Regenerate commit messages in HEAD
+$ git rebase --continue          # Repeat until the rebase is done
+
+$ git node land --final          # Verify all the commit messages
+```
+
 ## `get-metadata`
 
 This tool is inspired by Evan Lucas's [node-review](https://github.com/evanlucas/node-review),