Added test for check doc strings in crates.

#1856

crates/ra_cli/src/analysis_bench.rs

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

crates/ra_cli/src/analysis_stats.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 use std::{collections::HashSet, fmt::Write, path::Path, time::Instant};
 
 use ra_db::SourceDatabase;

crates/ra_cli/src/help.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 pub const GLOBAL_HELP: &str = "ra-cli
 
 USAGE:

crates/ra_cli/src/main.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 mod analysis_stats;
 mod analysis_bench;
 mod help;