Index: clang/www/get_started.html
===================================================================
--- clang/www/get_started.html
+++ clang/www/get_started.html
@@ -61,6 +61,9 @@
     <li><tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" ../llvm</tt></li>
     <li><tt>make</tt></li>
     <li>This builds both LLVM and Clang for debug mode.</li>
+    <li>Note: git does not ignore the build directory by default. You can add it
+        to <tt>.git/info/exclude</tt> to ignore it:
+        <tt>cd llvm-project && echo build >> .git/info/exclude</tt></li>
     <li>Note: For subsequent Clang development, you can just run
         <tt>make clang</tt>.</li>
     <li>CMake allows you to generate project files for several IDEs: Xcode,
Index: llvm/docs/GettingStarted.rst
===================================================================
--- llvm/docs/GettingStarted.rst
+++ llvm/docs/GettingStarted.rst
@@ -51,6 +51,12 @@
    * ``cd build``
    * ``cmake -G <generator> [options] ../llvm``
 
+     Note that git will not ignore the ``build`` directory by default. You can
+     add it to ``.git/info/exclude`` to ignore it:
+
+     * ``cd llvm-project``
+     * ``echo build >> .git/info/exclude``
+
      Some common generators are:
 
      * ``Ninja`` --- for generating `Ninja <https://ninja-build.org>`_