Add more information to README.

README.md

@@ -1,2 +1,37 @@
 # cargo-semver-checks-action
 A GitHub Action for running cargo-semver-checks
+
+By default, this action assumes that:
+- Your cargo workspace contains a single crate.
+- Your releases are tagged in git as `v{major}.{minor}.{patch}`, for example `v1.2.3`.
+
+Single-crate workspaces can use it as:
+```
+steps:
+- uses: actions/checkout@v3
+  with:
+    fetch-depth: 0
+- name: Check semver
+  uses: obi1kenobi/cargo-semver-checks-action@v1
+- name: Publish to crates.io
+  run: # your `cargo publish` code here
+```
+
+To use it in a workspace with more than one crate:
+- use the `crate-name` setting to specify which crate should be checked in a given run, and
+- use the `version-tag-prefix` setting to override the default prefix `v` to match the way the releases of your crate are tagged.
+
+For example, this is publishing `my-crate` whose releases are tagged as `my-crate-v1.2.3`:
+```
+steps:
+- uses: actions/checkout@v3
+  with:
+    fetch-depth: 0
+- name: Check semver
+  uses: obi1kenobi/cargo-semver-checks-action@v1
+  with:
+    crate-name: my-crate
+    version-tag-prefix: my-crate-v
+- name: Publish my-crate to crates.io
+  run: # your `cargo publish` code here
+```