Add readme.

README.md

@@ -0,0 +1,19 @@
+Online HNSW
+===========
+An implementation of the HNSW index for approximate nearest neighbors search for C++14,
+that supports incremental insertion and removal of elements.
+
+License
+=======
+Original parts of this project are licensed under the terms of the Apache 2.0 license.
+This project also includes:
+* A copy of
+[the hopscotch-map project](https://github.com/Tessil/hopscotch-map), which is licensed under the MIT license.
+It resides in `include/hnsw/containers/hopscotch-map-1.4.0`.
+* Parts of [nmslib](https://github.com/searchivarius/nmslib) which are also licensed under the Apache 2.0 license.
+
+Individual source files have corresponding copyright and license info.
+
+References
+==========
+* Malkov, Y.A., Yashunin, D.A. [Efficient and robust approximate nearest neighbor search using Hierarchical Navigable Small World graphs](https://arxiv.org/abs/1603.09320)

include/hnsw/index.hpp

@@ -353,7 +353,7 @@ struct hnsw_index {
         // I avoid use of uniform_real_distribution to control how many times random() is called.
         // This makes inserts reproducible across standard libraries.
 
-        // NOTE: This works fine for standard random engines because their value_type is required to be unsigned.
+        // NOTE: This works correctly for standard random engines because their value_type is required to be unsigned.
         auto sample = random() - random_t::min();
         auto max_rand = random_t::max() - random_t::min();