Show conditional enabling of caching

It took me a while to figure out how to use caching system on a condition, and set the relevant env vars.  Initially, I thought those env vars had to be set on the caching action itself, not on all the other actions -- this should be clarified too

README.md

@@ -19,6 +19,19 @@ Just copy and paste the following in your GitHub action:
   uses: mozilla-actions/sccache-action@v0.0.3
 ```
 
+### Conditionally run cache and enable it
+
+```
+- name: Run sccache-cache only on non-release runs
+  if: github.event_name != 'release' && github.event_name != 'workflow_dispatch'
+  uses: mozilla-actions/sccache-action@v0.0.3
+- name: Set Rust caching env vars only on non-release runs
+  if: github.event_name != 'release' && github.event_name != 'workflow_dispatch'
+  run: |
+    echo "SCCACHE_GHA_ENABLED=true" >> $GITHUB_ENV
+    echo "RUSTC_WRAPPER=sccache" >> $GITHUB_ENV
+```
+
 ### Specify a given version of sccache
 
 ```