Merge #210

210: Add `book.toml` file r=jamesmunns a=Rosto75

Metadata taken from https://github.com/rust-embedded/discovery/blob/master/README.md

Co-authored-by: Tomasz Różański <rosto@tlen.pl>

Author: bors[bot]

book.toml

@@ -0,0 +1,5 @@
+[book]
+title = "Discovery"
+description = "Discover the world of microcontrollers through Rust"
+author = "Rust Embedded Resources Team"
+language = "en"