Adding initial commit of the Concurrency Chapter

Author: borsakv

src/concurrency.md

@@ -0,0 +1,7 @@
+r[concurrency]
+# Concurrency
+
+r[concurrency.intro]
+Rust provides language and library features for writing concurrent programs. These features are designed to prevent data races — situations in which multiple threads access the same memory without proper synchronization, with at least one of the accesses modifying that memory.
+
+This chapter describes the traits, types, and concepts that Rust uses to express and enforce safe concurrency.

src/glossary.md

@@ -135,7 +135,7 @@ or not independent of applied type arguments. Given `trait Foo<T, U>`,
 A `struct`, `enum`, or `union` which was defined in the current crate.
 This is not affected by applied type arguments. `struct Foo` is considered local, but
 `Vec<Foo>` is not. `LocalType<ForeignType>` is local. Type aliases do not
-affect locality.
+affect locality. 
 
 ### Module