Improve README

README.md

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 # Birthdaze
 
+[View on RubyGems](https://rubygems.org/gems/birthdaze)
+
 Birthdaze is a tool to generate a calendar of your contacts’ birthdays
 from a CardDAV server account.
+
+## Installation
+
+```bash
+gem install ruby
+```
+
+Note Birthdaze relies on the `curb` gem, which requires `libcurl4-openssl-dev` to be installed.
+
+## Setup
+
+You’ll need a config file in the `~/.config/birthdaze.yaml` that looks like the below:
+
+```yaml
+username: <username>
+password: <password>
+url: <url>
+ical_output: <path to output file>
+```
+
+## Usage
+
+Print a list of all birthdays.
+```bash
+birthdaze list
+```
+
+Generate an iCalendar file of your contacts’ birthdays.
+
+## Notes
+
+* If a contact has a birthdate, the birthday will be set as recurring from that year. Otherwise,
+  it will be set as recurring from the current year.
+