update the README to document building with cmake

Summary:
Update the build steps in the README to build using cmake instead of autoconf
on Linux platforms.

I haven't updated the instructions for Mac OS X or the
`bootstrap-osx-homebrew.sh` script primarily because I have not tested the
steps on Mac.  It sounds like the build is close to working on Mac, but
currently fails due to missing compiler flags to disable some warnings on
clang.

Reviewed By: akushner

Differential Revision: D6780814

fbshipit-source-id: 9c9c211c306d5b35235549ae451bb620098f37e3

README.md

@@ -72,28 +72,34 @@ Folly is published on Github at https://github.com/facebook/folly
 
 folly requires gcc 4.9+ and a version of boost compiled with C++14 support.
 
-Please download googletest from
-https://github.com/google/googletest/archive/release-1.8.0.tar.gz and unpack it into the
-folly/test subdirectory as `gtest`:
+googletest is required to build and run folly's tests.  You can download
+it from https://github.com/google/googletest/archive/release-1.8.0.tar.gz
+The following commands can be used to download and install it:
 
-    (cd folly/test && \
-     rm -rf gtest && \
-     wget https://github.com/google/googletest/archive/release-1.8.0.tar.gz && \
-     tar zxf release-1.8.0.tar.gz && \
-     rm -f release-1.8.0.tar.gz && \
-     mv googletest-release-1.8.0 gtest)
+```
+wget https://github.com/google/googletest/archive/release-1.8.0.tar.gz && \
+tar zxf release-1.8.0.tar.gz && \
+rm -f release-1.8.0.tar.gz && \
+cd googletest-release-1.8.0 && \
+cmake configure . && \
+make && \
+make install
+```
 
-#### Linking non-default boost libraries
+#### Finding dependencies in non-default locations
 
-If you have boost installed in a non-default location, you need to be sure that
-the linker and configure scripts know where to find boost.  This means making
-sure that the `LIBRARY_PATH` environment variable contains `<BOOST_ROOT>/lib`,
-as well as including the path explicitly when running
-`./configure`:
+If you have boost, gtest, or other dependencies installed in a non-default
+location, you can use the `CMAKE_INCLUDE_PATH` and `CMAKE_LIBRARY_PATH`
+variables to make CMAKE look also look for header files and libraries in
+non-standard locations.  For example, to also search the directories
+`/alt/include/path1` and `/alt/include/path2` for header files and the
+directories `/alt/lib/path1` and `/alt/lib/path2` for libraries, you can invoke
+`cmake configure` as follows:
 
 ```
-export LIBRARY_PATH=$BOOST_ROOT/lib:$LIBRARY_PATH
-./configure --with-boost=$BOOST_ROOT/lib
+cmake configure \
+  -DCMAKE_INCLUDE_PATH=/alt/include/path1:/alt/include/path2 \
+  -DCMAKE_LIBRARY_PATH=/alt/lib/path1:/alt/lib/path2
 ```
 
 #### Ubuntu 16.04 LTS
@@ -104,10 +110,7 @@ command below):
 ```
 sudo apt-get install \
     g++ \
-    automake \
-    autoconf \
-    autoconf-archive \
-    libtool \
+    cmake \
     libboost-all-dev \
     libevent-dev \
     libdouble-conversion-dev \
@@ -136,11 +139,10 @@ sudo apt-get install \
 
 In the folly directory, run:
 ```
-  autoreconf -ivf
-  ./configure
-  make
-  make check
-  sudo make install
+  mkdir _build && cd _build
+  cmake configure ..
+  make -j $(nproc)
+  make install
 ```
 
 #### OS X (Homebrew)
@@ -207,21 +209,21 @@ You may also use `vcpkg install folly:x64-windows --head` to build against `mast
 - double-conversion (https://github.com/google/double-conversion)
 
   Download and build double-conversion.
-  You may need to tell configure where to find it.
+  You may need to tell cmake where to find it.
 
   [double-conversion/] `ln -s src double-conversion`
 
-  [folly/] `./configure LDFLAGS=-L$DOUBLE_CONVERSION_HOME/ CPPFLAGS=-I$DOUBLE_CONVERSION_HOME/`
+  [folly/] `mkdir build && cd build`
+  [folly/build/] `cmake configure "-DCMAKE_INCLUDE_PATH=$DOUBLE_CONVERSION_HOME/include" "-DCMAKE_LIBRARY_PATH=$DOUBLE_CONVERSION_HOME/lib" ..`
 
-  [folly/] `LD_LIBRARY_PATH=$DOUBLE_CONVERSION_HOME/ make`
+  [folly/build/] `make`
 
 - additional platform specific dependencies:
 
   Fedora 21 64-bit
     - gcc
     - gcc-c++
-    - autoconf
-    - autoconf-archive
+    - cmake
     - automake
     - boost-devel
     - libtool