Add docs for cache-write (#38)

.github/workflows/build.yml

@@ -42,7 +42,7 @@ jobs:
       - name: Assert latest setup-pixi version is mentioned in README
         run: |
           latest_version="$(jq -r '.version' package.json)"
-          count_expected=9
+          count_expected=10
           count_actual="$(grep -c "setup-pixi@v$latest_version" README.md || true)"
           if [ "$count_actual" -ne "$count_expected" ]; then
             echo "::error file=README.md::Expected $count_expected mentions of setup-pixi@v$latest_version in README.md, but found $count_actual."

README.md

@@ -25,7 +25,7 @@ GitHub Action to set up the [pixi](https://github.com/prefix-dev/pixi) package m
 ```yml
 - uses: prefix-dev/[email protected]
   with:
-    pixi-version: v0.5.0
+    pixi-version: v0.7.0
     cache: true
     auth-host: prefix.dev
     auth-token: ${{ secrets.PREFIX_DEV_TOKEN }}
@@ -52,6 +52,18 @@ You can specify the behavior by setting the `cache` input argument.
 If you need to customize your cache-key, you can use the `cache-key` input argument.
 This will be the prefix of the cache key. The full cache key will be `<cache-key><conda-arch>-<hash>`.
 
+#### Only save caches on `main`
+
+In order to not exceed the [10 GB cache size limit](https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#usage-limits-and-eviction-policy) as fast, you might want to restrict when the cache is saved.
+This can be done by setting the `cache-write` argument.
+
+```yml
+- uses: prefix-dev/[email protected]
+  with:
+    cache: true
+    cache-write: ${{ github.event_name == 'push' && github.ref_name == 'main' }}
+```
+
 ### Authentication
 
 There are currently three ways to authenticate with pixi: