doc: add basic install and usage instructions

README.md

@@ -1,3 +1,49 @@
 # [DuckDNS.sh](https://github.com/BeyondCodeBootcamp/DuckDNS.sh)
 
+A Posix Shell Script (Bash-compatible) for tracking your IP address
+(at home, or on devices).
 
+# Install
+
+```sh
+mkdir -p ~/bin/
+curl -fsSL -o ~/.local/bin/duckdns.sh https://raw.githubusercontent.com/BeyondCodeBootcamp/DuckDNS.sh/main/duckdns.sh
+chmod a+x ~/bin/duckdns.sh
+```
+
+# Configure
+
+You'll need to create your account, subdomain, and token before you can use `duckdns.sh`.
+
+1. Login to <https://duckdns.org>
+2. Create a subdomain, such as `CHANGE-ME` for `CHANGE-ME.duckdns.org`
+3. Copy your DNS Token
+4. Create your subdomain token file:
+    ```sh
+    mkdir -p ~/.config/duckdns.sh/
+    touch ~/.config/duckdns.sh/CHANGE_ME.env
+    ```
+5. Place your token in the file as `DUCKDNS_TOKEN=xxxxxxxx-YOUR-TOKEN...`:
+    ```sh
+    vim ~/.config/duckdns.sh/CHANGE_ME.env
+    ```
+    ```text
+    DUCKDNS_TOKEN=xxxxxxxx-xxxx-4xxx-8xxx-xxxxxxxxxxxx
+    ```
+
+# Usage
+
+```sh
+duckdns.sh run <subdomain>
+```
+
+# Examples
+
+```sh
+duckdns.sh run foo            # periodically check ip address and update subdomain
+```
+
+# License
+
+CC0-1.0 (Public Domain) \
+See <https://creativecommons.org/publicdomain/zero/1.0/>.