Mention 'pnpm' in docs

README.md

@@ -2,7 +2,7 @@
 
 A GitHub action that reports changes in compressed file sizes on your PRs.
 
-- Automatically uses `yarn` or `npm ci` when lockfiles are present
+- Automatically uses `yarn`, `pnpm` or `npm ci` when lockfiles are present
 - Builds your PR, then builds the target and compares between the two
 - Doesn't upload anything or rely on centralized storage
 - Supports [custom build scripts](#customizing-the-build) and [file patterns](#customizing-the-list-of-files)
@@ -161,4 +161,3 @@ By default, files are compared after gzip compression, but it's possible to use
 ```yaml
   compression: 'none'
 ```
-