docs(README): Update the README with new features

README.md

-# shift
+# shift [![pipeline status](https://gitlab.chromabits.com/etcinit/shift/badges/master/pipeline.svg)](https://gitlab.chromabits.com/etcinit/shift/-/commits/master)
 
-A changelog generator
+A changelog generator.
 
-## Usage
+## Overview
+
+`shift` is a Haskell library and executable that allow you to generate a changelog by inspecting the history of a Git repository.
+
+This project is somewhat a prototype, and mainly works if the repository being used meets the following criteria:
 
-This project is currently a prototype, and mainly works if you project meets
-the following criteria:
+- It's Git.
+- Commits follow the [Conventional Commits](https://www.conventionalcommits.org) spec or the [Angular Commit Convention](https://github.com/angular/angular/blob/master/CONTRIBUTING.md#-commit-message-format).
+- Version tags (vX.X.X.X, vX.X.X, and others).
+- It's hosted on a GitLab instance or GitHub, if links to commits and authors are desired.
 
-- It is on Git.
-- Commits follow the Angular commit convention.
-- Numeric tags (vX.X.X.X, vX.X.X, and others).
-- For URLs to authors and commits, it will need to be hosted on GitHub.
+The `shift` executable generates changelogs in Markdown. However, the underlying data structure can be accessed on the library version for custom processing.
 
-If it does, you can build and install this project using Stack:
+## Installing
+
+You can build and install this project using Stack:
 
 ```
 stack build --copy-bins
 ```
 
+## Usage
+
 Once `shift`, is in your `PATH`, you can invoke it according to where your
 repository is hosted:
 
+- **GitLab:**
+
+  ```
+  shift generate -t gitlab --gitlab-token XXX --gitlab-owner etcinit --gitlab-repository shift --gitlab-server https://gitlab.chromabits.com
+  ```
+
 - **GitHub:**
 
+  ```
+  shift generate -t github --github-token XXX --github-owner etcinit --github-repository shift
+  ```
+
+- **Local/Other:**
+
+  ```
+  shift generate -t git
+  ```
+
+To generate a `CHANGELOG` file, use: `shift -t git generate --output-path CHANGELOG`.
+
+### Options
+
+| Name | Description | Example |
+| --- | --- | --- |
+| `--output-path` | Writes the generated chagelog to the specified path. Note: The path will be overwritten one every run. | - |
+| `--include-head` | Whether to include `HEAD` as a version in the changelog. Useful for tracking changes for the next tag. | - |
+| `--from-ref` | The starting point of the changelog. If `--to-ref` is also specified, the changelog will be generated from the diff between these two refs.  | `v1.0.1` |
+| `--to-ref` | The end point of the changelog. If `--from-ref` is also specified, the changelog will be generated from the diff between these two refs.  | `v1.0.1` |
+
+### Built-in Server
+
+`shift` also has a built-in web server for quickly previewing changes. Every refresh causes the changelog to be regenerated.
+
 ```
-shift generate -t github --github-token XXX --github-owner etcinit --github-repository shift
+shift serve -t git
 ```
 
-- **Local/Other:** `shift generate -t git`.
-
-To save to a `CHANGELOG.md` file: `shift generate -t git > CHANGELOG.md`.
+Navigate to http://localhost:3000 to view the changelog.
 
-## TODO
+By default, it will be rendered to HTML. A `as_markdown=true` query string param can be specified to view the changelog as Markdown: http://localhost:3000?as_markdown=true
 
-A lot.
+#### Options
 
-- Other hosting types: Phabricator, BitBucket.
-- Support more commit conventions.
-- Templates.
-- Releases.
+| Name | Description | Example |
+| --- | --- | --- |
+| `--port` | The port to start the HTTP listener in. Defaults to `3000` if not provided. | `4000` |