Document min CMake version
## Proposed Changes
Add a tip about the minimum CMake version to make it more obvious what it takes to compile on Ubuntu 18.04.
@@ -19,6 +19,10 @@ Install the following packages:
sudo apt install -y git gcc g++ make cmake pkg-config llvm-dev libclang-dev clang
```
+> Note: Lighthouse requires CMake v3.12 or newer, which isn't available in the package repositories
+> of Ubuntu 18.04 or earlier. On these distributions CMake can still be installed via PPA:
+> [https://apt.kitware.com/](https://apt.kitware.com)
+
#### macOS
1. Install the [Homebrew][] package manager.
