diff --git a/README.md b/README.md
index 5b79d1fb..0417e6f7 100644
--- a/README.md
+++ b/README.md
@@ -36,6 +36,7 @@ of the selected architecture:
 - Python 3.5 or later, including development libraries (`python3-dev` for Ubuntu)
   - on Windows make sure to install same version as supported by [vcpkg](https://github.com/Microsoft/vcpkg/blob/master/ports/python3/CONTROL)
 - Boost libraries (`libboost-dev libboost-filesystem-dev libboost-thread-dev libboost-program-options-dev libboost-python-dev libboost-dev` or `libboost-all-dev` for Ubuntu)
+- Eigen3 (`libeigen3-dev` for Ubuntu) is required to build the analytic placer
 - Latest git Yosys is required to synthesise the demo design
 - For building on Windows with MSVC, usage of vcpkg is advised for dependency installation.
   - For 32 bit builds: `vcpkg install boost-filesystem boost-program-options boost-thread boost-python qt5-base`
@@ -119,11 +120,11 @@ Use cmake `-D` options to specify which version of nextpnr you want to build.
 Use `-DARCH=...` to set the architecture. It is a semicolon separated list.
 Use `cmake . -DARCH=all` to build all supported architectures.
 
-The following runs a debug build of the iCE40 architecture without GUI
-and without Python support and only HX1K support:
+The following runs a debug build of the iCE40 architecture without GUI,
+ without Python support, without the HeAP analytic placer and only HX1K support:
 
 ```
-cmake -DARCH=ice40 -DCMAKE_BUILD_TYPE=Debug -DBUILD_PYTHON=OFF -DBUILD_GUI=OFF -DICE40_HX1K_ONLY=1 .
+cmake -DARCH=ice40 -DCMAKE_BUILD_TYPE=Debug -DBUILD_PYTHON=OFF -DBUILD_GUI=OFF -DBUILD_HEAP=OFF -DICE40_HX1K_ONLY=1 .
 make -j$(nproc)
 ```
 
@@ -134,6 +135,9 @@ cmake -DARCH=ice40 -DBUILD_PYTHON=OFF -DBUILD_GUI=OFF -DSTATIC_BUILD=ON .
 make -j$(nproc)
 ```
 
+The HeAP placer's solver can optionally use OpenMP for a speedup on very large designs. Enable this by passing
+`-DUSE_OPENMP=yes` to cmake (compiler support may vary).
+
 You can change the location where nextpnr will be installed (this will usually default to `/usr/local`) by using
 `-DCMAKE_INSTALL_PREFIX=/install/prefix`.