Added test for check doc strings in crates.

#1856

crates/ra_project_model/src/cargo_workspace.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 use std::path::{Path, PathBuf};
 
 use cargo_metadata::{CargoOpt, MetadataCommand};

crates/ra_project_model/src/json_project.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 use std::path::PathBuf;
 
 use serde::Deserialize;

crates/ra_project_model/src/lib.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 mod cargo_workspace;
 mod json_project;
 mod sysroot;

crates/ra_project_model/src/sysroot.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 use std::{
     env,
     path::{Path, PathBuf},