Describe buildenv in EESSI docs (#845)

* draft of eessi docs

* second draft of eessi doc

* third draft of docs

* Fix typo in EESSI documentation

* third draft of docs

* final draft of eessi docs

* fixing linting

* adding buildenv module section to eessi docs

Author: claudia-lola

docs/eessi.md

@@ -4,7 +4,7 @@
 
 The EESSI environment can be initialise by running:
 
-```[bash]
+```bash
 source /cvmfs/software.eessi.io/versions/2023.06/init/bash
 ```
 
@@ -30,6 +30,8 @@ To deactivate your EESSI environment you can either restart your shell using `ex
 
 To enable GPU support, the cluster must be running a site-specific image build that has CUDA enabled. For a guide on how to do this, please refer to [docs/image-build.md](../image-build.md).
 
+More information about EESSI GPU Support can be found in the [EESSI docs](https://www.eessi.io/docs/site_specific_config/gpu/).
+
 ### Using GPUs
 
 All CUDA-enabled software in EESSI expects CUDA drivers in a specific `host_injections` directory.
@@ -38,7 +40,7 @@ All CUDA-enabled software in EESSI expects CUDA drivers in a specific `host_inje
 
 Use the `link_nvidia_host_libraries.sh` script, provided by EESSI, to symlink your GPU drivers into `host_injections`.
 
-```[bash]
+```bash
 /cvmfs/software.eessi.io/versions/2023.06/scripts/gpu_support/nvidia/link_nvidia_host_libraries.sh
 ```
 
@@ -50,43 +52,55 @@ Run `which nvcc` to confirm that the CUDA compiler is found.
 
 If `nvcc` is not found, add the CUDA path to your environment:
 
-```[bash]
+```bash
 export PATH=/usr/local/cuda/bin:$PATH
 ```
 
 `which nvcc` should now show the path to the CUDA compiler.
 
-#### Loading EESSI module for the GCC compiler
+#### Loading EESSI buildenv module
+
+The `buildenv` module provides the environment needed to build software with EESSI. The module sets up compiler and linker wrappers to ensure the builds are linked to the correct EESSI libraries. This means that the program can run even without the EESSI environment loaded.
+
+To load the `buildenv` module, run:
+
+```bash
+module load buildenv/default-foss-2023b
+```
+
+Now you can run `cmake` and `make` to compile CUDA programs using EESSI's modules loaded by `buildenv`.
 
-Running `which gcc` with EESSI initialised should initially show a path `.../2023.06/compat...` which points to the compatibility compiler.
+Additional modules may need to be loaded to compile programs. To see available modules to load in EESSI run:
 
-It is important to load a `gcc` version that is compatible with the host's CUDA version. This can be found by referring to the table below:
+```bash
+module avail
+```
 
-To find your cuda version run `nvcc --version`
+#### Useful EESSI Commands
 
-| **CUDA Version** | **Recommended GCC Module (EESSI 2023.06)**              |
-| ---------------- | ------------------------------------------------------- |
-| CUDA 13.0        | GCC/12.3.0                                              |
-| CUDA 12.3 – 12.5 | GCC/12.3.0 or GCC/12.2.0 (officially supports GCC 12.x) |
-| CUDA 12.0 – 12.2 | GCC/12.2.0 (officially listed supported version)        |
-| CUDA 11.4 – 11.8 | no matching GCC module in EESSI 2023.06                 |
-| CUDA < 11.4      | not supported                                           |
+To see modules currently loaded in EESSI, run:
 
-To load correct ESSI module run, substituting x for the compatible GCC version:
+```bash
+module list
+```
 
-```[bash]
-module load GCC/12.x.0
+To unload all currently loaded modules:
+
+```bash
+module purge
 ```
 
-Running `which gcc` will now give a path `.../2023.06/software...` which is the full compiler provided by EESSI. This is what we want for CUDA builds.
+To unload a specific module, run (e.g GCC/12.3.0):
 
-Now you can run `cmake` and `make` to compile CUDA using EESSI's `gcc`.
+```bash
+module unload GCC/12.3.0
+```
 
 #### Test: Compile deviceQuery from CUDA-Samples
 
 To test that your EESSI setup can compile CUDA, try compiling `deviceQuery` from CUDA-Samples with the following steps:
 
-```[bash]
+```bash
 git clone https://github.com/NVIDIA/cuda-samples.git
 cd cuda-samples/Samples/1_Utilities/deviceQuery
 mkdir -p build