Document how to publish

Author: taiki-e

Cargo.toml

@@ -1,5 +1,9 @@
 [package]
 name = "trajectory"
+# When publishing a new version:
+# - Create "v0.x.y" git tag
+# - Push the above tag (run `git push origin --tags`)
+# Then, CI will publish to crates.io and create a GitHub release.
 version = "0.1.0"
 authors = ["Takashi Ogura <t.ogura@gmail.com>"]
 edition = "2021"