README: Update lab build depednencies (NVIDIA#298)

* README: Lab requires python3 devel headers/library

The python3 development headers and library are required, or else
llama-cpp-python fails to build.

    × Building wheel for llama-cpp-python (pyproject.toml) did not run successfully.
    │ exit code: 1
    ╰─> [23 lines of output]
        *** scikit-build-core 0.8.2 using CMake 3.28.3 (wheel)
        *** Configuring CMake...
        2024-03-05 11:42:14,297 - scikit_build_core - WARNING - libdir/ldlibrary: /usr/lib64/libpython3.12.so is not a real file!
        2024-03-05 11:42:14,297 - scikit_build_core - WARNING - Can't find a Python library, got libdir=/usr/lib64, ldlibrary=libpython3.12.so, multiarch=x86_64-linux-gnu, masd=None

Signed-off-by: Stef Walter <stefw@redhat.com>

* README: Add gh tool install command on Fedora Linux

This is required to download the model.

Signed-off-by: Stef Walter <stefw@redhat.com>

* README: Command to install the g++ compiler on Fedora Linux

Add the command to install the g++ compiler on Fedora Linux. Otherwise
we get an error similar to the following when building llama-cpp-python

    × Building wheel for llama-cpp-python (pyproject.toml) did not run successfully.
    │ exit code: 1
    ╰─> [21 lines of output]
        *** scikit-build-core 0.8.2 using CMake 3.28.3 (wheel)
        *** Configuring CMake...
        loading initial cache file /tmp/tmppdxr1vom/build/CMakeInit.txt
        -- The C compiler identification is GNU 14.0.1
        -- The CXX compiler identification is unknown
        -- Detecting C compiler ABI info
        -- Detecting C compiler ABI info - done
        -- Check for working C compiler: /usr/bin/cc - skipped
        -- Detecting C compile features
        -- Detecting C compile features - done
        CMake Error at CMakeLists.txt:3 (project):
          No CMAKE_CXX_COMPILER could be found.

Signed-off-by: Stef Walter <stefw@redhat.com>

---------

Signed-off-by: Stef Walter <stefw@redhat.com>

README.md

@@ -17,9 +17,16 @@ After that is done you can:
 ## 📋 Requirements
 
 - **🍎 Apple M1/M2/M3 Mac or 🐧 Linux system** (tested on Fedora). We anticipate support for more operating systems in the future.
-- 🐍 Python 3.9 or later
+- The GNU C++ compiler
+- 🐍 Python 3.9 or later, including the development headers.
 - `gh` cli: Install [Github command cli](https://cli.github.com/) for downloading models from Github
 
+On Fedora Linux this means installing:
+```
+$ sudo dnf config-manager --add-repo https://cli.github.com/packages/rpm/gh-cli.repo
+$ sudo yum install g++ gh python3 python3-devel
+```
+
 ## 🧰 Installing `lab`
 
 To start we'll create a new directory called `instruct-lab` to store the files that this CLI needs when it runs.