Customize Netlify ignore to build for Readme.md changes

Author: messense

netlify.toml

@@ -2,3 +2,4 @@
   base = "guide"
   publish = "book/"
   command = "curl -L https://github.com/rust-lang/mdBook/releases/download/v0.4.13/mdbook-v0.4.13-x86_64-unknown-linux-gnu.tar.gz | tar xvz && ./mdbook build"
+  ignore = "git diff --quiet $CACHED_COMMIT_REF $COMMIT_REF . ../Readme.md"