Document how to use FlowCrafter in README (#28)

An initial pass at some documentation has been done in the project's
README. It describes how to create templates, initialize FlowCrafter in
a project, and then use it to generate workflows.

README.md

@@ -3,6 +3,126 @@
 FlowCrafter is a command-line tool to create and manage workflows for
 [GitHub Actions].
 
+## Installation
+
+FlowCrafter can be installed using `cargo`. Running the following command will
+download the latest version of FlowCrafter, compile it, and make it available as
+a command-line tool.
+
+```shell
+cargo install flowcrafter
+```
+
+After the installation, `flowcrafter` is available as a command in the terminal:
+
+```shell
+flowcrafter --help
+```
+
+## Usage
+
+Using FlowCrafter consists of three different steps:
+
+1. [Creating templates for workflows and jobs](#create-templates)
+2. [Initializing FlowCrafter in a repository](#initialize-flowcrafter)
+3. [Creating and updating workflows](#create-a-workflow)
+
+### Create Templates
+
+FlowCrafter uses templates stored on GitHub to create workflows and jobs. These
+are YAML files that follow a few conventions:
+
+- The repository contains a folder for each workflow (e.g. `rust`).
+- Each workflow folder contains a file called `workflow.yml` that defines the
+  workflow (e.g. `rust/workflow.yml`).
+- Job templates are stored in the same folder as the workflow file (e.g.
+  `rust/lint.yml`).
+
+#### Workflow
+
+The workflow template sets the top-level configuration for the workflow. It can
+also contain a list of jobs that should always be part of the workflow.
+
+The workflow template is always named `workflow.yml`.
+
+```yaml
+---
+name: Rust
+
+"on":
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  run-always:
+    name: Always include this job
+    runs-on: ubuntu-latest
+
+    steps:
+      - run: echo "This will always be included"
+```
+
+#### Jobs
+
+Jobs are defined in individual YAML files within the workflow folder. Each
+represents a single job that can be included in a workflow.
+
+```yaml
+style:
+  name: Check style
+  runs-on: ubuntu-latest
+
+  steps:
+    - name: Checkout code
+      uses: actions/checkout@v3
+
+    - name: Run Rustfmt
+      run: cargo fmt --all -- --check
+```
+
+### Initialize FlowCrafter
+
+FlowCrafter manages the workflows for a repository on GitHub. After cloning the
+repository to your local machine, open a terminal, change into its directory,
+and then generate a configuration file for FlowCrafter:
+
+```shell
+flowcrafter init -r <owner>/<repo>
+```
+
+This will create a file called `.flowcrafter.yml` in the `.github` directory and
+configure the repository `owner/repo` as the source for workflow and job
+templates.
+
+### Create a Workflow
+
+With FlowCrafter initialized and templates on GitHub, you can now create a
+workflow with FlowCrafter:
+
+```shell
+flowcrafter create -w <workflow> -j <job> -j <job>
+```
+
+For example, given a repository with the following templates:
+
+```text
+rust
+├── lint.yml
+├── test.yml
+└── workflow.yml
+```
+
+You can create a workflow for Rust with the following command:
+
+```shell
+flowcrafter create -w rust -j lint -j test
+```
+
+This will create the file `.github/workflows/rust.yml` and merge `workflow.yml`
+and the two jobs `lint.yml` and `test.yml` into it.
+
 ## License
 
 Licensed under either of