Add readme

Author: anderspitman

cmd/patchbay-cli/README.md

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+This is a CLI companion tool for the patchbay.pub web service.
+
+It is still very early in development. See main.go for all functionality and
+uses.
+
+To host a static site, run something like the following from the root directory
+of the site:
+
+```
+patchbay-cli host -root-channel https://patchbay.pub/my-secret-channel
+```
+
+You can then navigate to `https://patchbay.pub/my-secret-channel/` in your
+browser. Don't forget the trailing slash, or use the full /index.html URL.
+This is necessary for relative URLs to work properly in browsers.