docs: extend README

README.md

@@ -1,10 +1,10 @@
 pre-commit-ast-grep
 [![tag](https://img.shields.io/github/v/tag/boidolr/pre-commit-ast-grep?sort=semver)](https://github.com/boidolr/pre-commit-ast-grep/tags)
-[![pre-commit](https://img.shields.io/badge/pre--commit-enabled-brightgreen?logo=pre-commit&logoColor=white)](https://github.com/pre-commit/pre-commit)
+[![pre-commit](https://img.shields.io/badge/pre--commit-hook-brightgreen?logo=pre-commit&logoColor=white)](https://github.com/pre-commit/pre-commit)
 ================
 
 
-Minimal git hooks to run [`ast-grep`](https://github.com/ast-grep/ast-grep) based on the [pre-commit](https://github.com/pre-commit/pre-commit) framework.
+Minimal git hook to run [ast-grep](https://github.com/ast-grep/ast-grep) based on the [pre-commit](https://github.com/pre-commit/pre-commit) framework.
 
 ## Using pre-commit-ast-grep with pre-commit
 
@@ -16,16 +16,22 @@ Add this to your `.pre-commit-config.yaml`:
       - id: ast-grep
 ```
 
+Note that only rules with a severity of "error" will trigger the commit hook.
+
+
 ### Automatically execute rewrites
 
 ```
   - repo: https://github.com/boidolr/pre-commit-ast-grep
     rev: v0.2.0  # Use the ref you want to point at
     hooks:
       - id: ast-grep
-          args: ["--update-all"]
+        args: ["--update-all"]
 ```
 
+Mixing rules with fixes and without fixes with the "--update-all" option is currently not supported.
+
+
 ### Provide explicit configuration
 
 ```
@@ -36,6 +42,7 @@ Add this to your `.pre-commit-config.yaml`:
         args: ["--config", "/some/path/sgconfig.yaml"]
 ```
 
+
 ## How to write rules
 
 See https://ast-grep.github.io/ for details on `ast-grep` and how to write linters and rewriters.