Document the building process.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=192490601

README.md

@@ -5,6 +5,7 @@
 Authors: Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
 
 # Features
+
   * Keys and values are arbitrary byte arrays.
   * Data is stored sorted by key.
   * Callers can provide a custom comparison function to override the sort order.
@@ -16,15 +17,30 @@ Authors: Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
   * External activity (file system operations etc.) is relayed through a virtual interface so users can customize the operating system interactions.
 
 # Documentation
-  [LevelDB library documentation](https://github.com/google/leveldb/blob/master/doc/index.md) is online and bundled with the source code.
 
+  [LevelDB library documentation](https://github.com/google/leveldb/blob/master/doc/index.md) is online and bundled with the source code.
 
 # Limitations
+
   * This is not a SQL database.  It does not have a relational data model, it does not support SQL queries, and it has no support for indexes.
   * Only a single process (possibly multi-threaded) can access a particular database at a time.
   * There is no client-server support builtin to the library.  An application that needs such support will have to wrap their own server around the library.
 
+# Building
+
+This project supports [CMake](https://cmake.org/) out of the box.
+
+Quick start:
+
+```bash
+mkdir -p build && cd build
+cmake -DCMAKE_BUILD_TYPE=Release .. && cmake --build .
+```
+
+Please see the CMake documentation and `CMakeLists.txt` for more advanced usage.
+
 # Contributing to the leveldb Project
+
 The leveldb project welcomes contributions. leveldb's primary goal is to be
 a reliable and fast key/value store. Changes that are in line with the
 features/limitations outlined above, and meet the requirements below,
@@ -45,6 +61,7 @@ Contribution requirements:
    a sufficient explanation as to why a new (or changed) test is not required.
 
 ## Submitting a Pull Request
+
 Before any pull request will be accepted the author must first sign a
 Contributor License Agreement (CLA) at https://cla.developers.google.com/.