Small documentation improvements.

- Highlighted that libcuckoo is a header-only library.

- Suggest passing in an aligned allocator, since our spinlock is 64-byte
  aligned.

README.md

@@ -34,6 +34,11 @@ support for atomic operations. Building the library requires CMake version >=
 Building
 ==========
 
+libcuckoo is a header-only library, so in order to get going, just add the
+`libcuckoo` subdirectory to your include path. These directions cover
+installing the library to a particular location on your system, and also
+building any the examples and tests included in the repository.
+
 We suggest you build out of source, in a separate `build` directory:
 
     $ mkdir build

libcuckoo/cuckoohash_map.hh

@@ -34,7 +34,9 @@
  * @tparam T type of values in the table
  * @tparam Hash type of hash functor
  * @tparam KeyEqual type of equality comparison functor
- * @tparam Allocator type of allocator
+ * @tparam Allocator type of allocator. We suggest using an aligned allocator,
+ * because the table relies on types that are over-aligned to optimize
+ * concurrent cache usage.
  * @tparam SLOT_PER_BUCKET number of slots for each bucket in the table
  */
 template <class Key, class T, class Hash = std::hash<Key>,