Updated lintrunner (markdown)

lintrunner.md

@@ -6,15 +6,39 @@ pip install lintrunner
 lintrunner init
 ```
 This will install `lintrunner` on your system and download all the necessary dependencies to run linters locally. Note that this will install new packages with `pip` and download binaries maintained by the PyTorch team. If you want to see what `lintrunner init` will install, run `lintrunner init --dry-run`.
-
-After that, you can do:
+### How do I run linters locally?
 ```
 lintrunner
 ```
-to lint your local changes, or
+to lint your local changes (by default, this is your working tree changes and the HEAD commit).
+### How do I autoformat my code?
 ```
 lintrunner f
 ```
-to autoformat your changes.
+to format locally changed files.
+### How do I run lint on my entire PR/branch?
+If, say, your PR is targeting `master`, run:
+```
+lintrunner -m master
+```
+### How do I run lint on specific files?
+```
+lintrunner torch/jit/_script.py torch/jit/_trace.py
+```
+`xargs` also works fine:
+```
+find -type f torch/onnx | xargs lintrunner
+```
+### How do I run lint on every file?
+```
+lintrunner --paths-cmd='git grep -Il .'
+```
+(or use `xargs`).
+### How do I run only a specific linter?
+```
+lintrunner --take BLACK,CLANGFORMAT
+```
+To see what linter names to pass, consult the [config](https://github.com/pytorch/pytorch/blob/master/.lintrunner.toml). By default, `lintrunner` runs all linters. To skip a linter, use `--skip`.
+### I have another question
 
 For more docs run `lintrunner --help`, or see [the `lintrunner` repo](https://github.com/suo/lintrunner).