Update README.md

Author: matthew-olson-intel

README.md

@@ -46,17 +46,23 @@ on your system:
 1. CMake
 2. Clang
 3. LLVM (e.g. `llvm-strip`)
-4. `bpftool`
 5. NCURSES
 6. POSIX Threads
 7. `libelf`
 
 You can install these on Ubuntu 20.04, 21.10, or 22.04 by issuing the following:
 ```
 sudo apt-get update
-sudo apt-get install libelf-dev cmake clang llvm linux-tools-generic
+sudo apt-get install libelf-dev cmake clang llvm llvm-dev
 ```
 
+Ubuntu 18.04 requires a bit more work; the default LLVM version is too old:
+```
+sudo apt-get update
+sudo apt-get install libelf-dev cmake clang-10 llvm-10 llvm-10-dev
+```
+Then edit `build.sh` and append `-10` to the values of `CLANG`, `CLANGXX`, and `LLVMSTRIP`.
+
 On CentOS 8.4, CentOS 8 Stream, and CentOS 9 Stream:
 ```
 sudo yum update