update macos binary; update readme

README.md

@@ -5,3 +5,45 @@ characters with other unicode characters, and sometimes deletes characters and
 sends them off into the internet over UDP ECHO packets.
 
 This program is used in a poetry project that lives here: [tilde.town/~ike/rot.html](https://tilde.town/~ike/rot.html)
+
+## Usage
+
+Before using this program, you need to have a poem file ready. This is a plain text file.
+
+To use this program in production, run the binary with the the first parameter as the poem file, and the second parameter as the html file to update. For example:
+
+```
+$ rot ~/poem.txt /var/www/rot.html
+```
+
+To use this program in development, you can run it with `go run`:
+
+```
+$ go run main.go poem.txt test.html
+```
+
+Every time this program runs, it will take the contents of the poem file, "rot"
+it using its algorithm, write the contents to the html file, and then update the
+poem file with the new rotted contents.
+
+One way to automate this is to use a [cron job](https://crontab.guru/) that runs 
+on a regular interval, for example, every hour:
+
+```
+0 * * * * /path/to/rot /path/to/poem.txt /path/to/rot.html
+```
+
+## Development
+
+To build the program, make sure you have [Go](https://golang.org/dl/) installed.
+These instructions assume you have Go 1.24 or later, and are running on macOS.
+
+Then, clone this repository and run:
+```
+$ go build -o dist/rot-darwin .
+```
+
+To build for linux, run:
+```
+$ CC=x86_64-unknown-linux-gnu-gcc CGO_ENABLED=1 GOARCH=amd64 GOOS=linux go build  -ldflags '-linkmode external -w -extldflags "-static"' -o dist/rot-linux_amd64 .
+```