README: Document mdl and vale

Signed-off-by: Philip Molloy <philip@philipmolloy.com>

Author: pamolloy

README.md

@@ -15,6 +15,16 @@ This book is written with [mdBook](https://github.com/rust-lang/mdBook).
 When installed, run `mdbook serve` and you will get a local webserver.
 For more details, please refer to the mdBook documentation.
 
+The book is linted with markdownlint and Vale. Follow the official
+documentation to [install
+markdownlint](https://github.com/markdownlint/markdownlint?tab=readme-ov-file#installation)
+and [install Vale](https://vale.sh/docs/install). Then run `vale sync` to
+download the necessary styles.
+
+From the root directory of the repository run `mdl /src/example.md` and `vale
+src/example.md`. Add words that trigger false positive spelling errors to
+`ci/vale/styles/config/vocabularies/LinuxBoot/accept.txt`.
+
 ## Acknowledgments
 
 In alphabetical order: