docs: slim down readme (#2140)

* docs: move docs table of contents to docs/index.md

* docs: move how it works and IDE support to about.md

* docs: move readme steps to walkthrough

* docs: slim down readme

* refactor: walkthrough -> quickstart

* docs: minor edits

docs/quickstart.md

@@ -0,0 +1,37 @@
+# Quickstart
+
+This guide will walk you through creating your first template and workspace. If you haven't already installed `coder`, do that first [here](./install.md).
+
+## Creating your first template and workspace
+
+In a new terminal window, run the following to copy a sample template:
+
+```bash
+coder templates init
+```
+
+Follow the CLI instructions to modify and create the template specific for your
+usage (e.g., a template to **Develop in Linux on Google Cloud**).
+
+Create a workspace using your template:
+
+```bash
+coder create --template="yourTemplate" <workspaceName>
+```
+
+Connect to your workspace via SSH:
+
+```bash
+coder ssh <workspaceName>
+```
+
+## Modifying templates
+
+If needed, you can edit the Terraform template using a sample template:
+
+```sh
+coder templates init
+cd gcp-linux/
+vim main.tf
+coder templates update gcp-linux
+```