Add tips for building MLIR and OpenFHE on low-RAM systems

Author: FlorentCLMichel

docs/content/en/docs/development.md

@@ -206,6 +206,65 @@ Based on what you're trying to do, this may require some extra steps.
 Send any upstream changes to HEIR-relevant MLIR files to @j2kun (Jeremy Kun) who
 has LLVM commit access and can also suggest additional MLIR reviewers.
 
+## Tips for building dependencies / useful external libraries
+
+### MLIR
+
+Instructions for building MLIR can be found on the
+[Getting started](https://mlir.llvm.org/getting_started/) page of the MLIR
+website. The instructions there seem to work as written (tested on Ubuntu
+22.04). However, the command shown in `Unix-like compile/testing:` may require a
+large amount of RAM. If building on a system with 16GB of RAM or less, and if
+you don't plan to target GPUs, you may want to replace the line
+
+```
+   -DLLVM_TARGETS_TO_BUILD="Native;NVPTX;AMDGPU" \
+```
+
+with
+
+```
+   -DLLVM_TARGETS_TO_BUILD="Native" \
+```
+
+### OpenFHE
+
+A simple way to build OpenFHE is to follow the instructions in the
+[openfhe-configurator](https://github.com/openfheorg/openfhe-configurator)
+repository. This allows to build the library with or without support for the
+Intel [HEXL library](https://github.com/intel/hexl). First, clone the repository
+and configure it using:
+
+```
+git clone https://github.com/openfheorg/openfhe-configurator.git
+cd openfhe-configurator
+scripts/configure.sh
+```
+
+You will be asked whether to stage a vanilla OpenFHE build or add support for
+HEXL. You can then build the library using
+
+```
+./scripts/build-openfhe-development.sh
+```
+
+The build may fail on systems with less than 32GB or RAM due to parallel
+compilation. You can disable it by editing
+`./scripts/build-openfhe-development.sh` and replacing
+
+```
+make -j || abort "Build of openfhe-development failed."
+```
+
+with
+
+```
+make || abort "Build of openfhe-development failed."
+```
+
+Compilation will be significantly slower but should then take less than 8GB of
+memory.
+
 ## Creating a New Pass
 
 The `scripts/templates` folder contains Python scripts to create boilerplate for