1377 provide RHEL installation instructions (#1378)

* added RHEL install and build instructions #1377

* updates per PR review feedback #1377

INSTALL.md

@@ -6,9 +6,10 @@ This guide will walk you through the environment configuration for Arkouda to op
 # Table of Contents
 
 1. [General Requirements](#genreqs)
-2. [Linux (Ubuntu)](#linux-ubuntu)
-   1. [Install Chapel](#lu-chapel)
-   2. [Python Envrionment](#lu-python)
+2. [Linux](#linux)
+   1. [Install Chapel (Ubuntu)](#lu-chapel)
+   2. [Install Chapel (RHEL)](#rhel-chapel)
+   3. [Python Envrionment](#l-python)
 3. [Windows](#windows)
 4. [MacOS](#mac)
    1. [Homebrew Installation](#mac-brew)
@@ -25,6 +26,7 @@ This guide will walk you through the environment configuration for Arkouda to op
 <a id="genreqs"></a>
 ## Requirements: <sup><sup><sub><a href="#toc">toc</a></sub></sup></sup>
  * chapel 1.25.1 or 1.26.0 (Recommended)
+ * cmake >= 3.11.0
  * zeromq version >= 4.2.5, tested with 4.2.5 and 4.3.1
  * hdf5 
  * python 3.7 or greater
@@ -35,14 +37,14 @@ This guide will walk you through the environment configuration for Arkouda to op
  * sphinx, sphinx-argparse, and sphinx-autoapi to generate docs
  * versioneer for versioning
 
-<a id="linux-unbuntu"></a>
-## Linux (Ubuntu)<sup><sup><sub><a href="#toc">toc</a></sub></sup></sup>
+<a id="linux"></a>
+## Linux<sup><sup><sub><a href="#toc">toc</a></sub></sup></sup>
+
+There is no Linux Chapel install, so the first two steps in the Linux Arkouda install are to install the Chapel dependencies followed by downloading and building Chapel. The Ubuntu and RHEL Chapel installations are different for installing Chapel dependencies, particularly regarding older RHEL distro versions such as CentOS 7. Specifically, the gcc compiler on RHEL distros such as CentOS 7 do not support building Chapel. Consequently, a newer version of the gcc compiler must be installed via the [devtoolset-9-gcc-c++](https://centos.pkgs.org/7/centos-sclo-rh-x86_64/devtoolset-9-gcc-c++-9.1.1-2.6.el7.x86_64.rpm.html) package. In addition, the CentOS [Software Collections packager](https://wiki.centos.org/AdditionalResources/Repositories/SCL) must be installed to enable the newer version of gcc to be leveraged for building Chapel.
 
 <a id="lu-chapel"></a>
 ### Install Chapel (Ubuntu)<sup><sup><sub><a href="#toc">toc</a></sub></sup></sup>
 
-There is no Linux Chapel install, so the first two steps in the Linux Arkouda install are to install the Chapel dependencies followed by downloading and building Chapel.
-
 ```bash
 # Update Linux kernel and install Chapel dependencies
 sudo apt-get update
@@ -84,8 +86,32 @@ make chpldoc
 export PATH=$CHPL_HOME/bin/linux64-x86_64/:$PATH
 ```
 
-<a id="lu-python"></a> 
-### Python Environment - Anaconda (Ubuntu)<sup><sup><sub><a href="#toc">toc</a></sub></sup></sup>
+<a id="rhel-chapel"></a>
+### Install Chapel (RHEL)<sup><sup><sub><a href="#toc">toc</a></sub></sup></sup>
+
+For all RHEL distros, Chapel dependencies are installed as follows:
+
+```
+yum update -y && yum install gcc gcc-c++ m4 perl python3 python3-devel \
+make gawk git cmake llvm-devel clang clang-devel curl-devel -y
+```
+
+For older RHEL distros with incompatible gcc compiler versions, the following dependencies must be installed:
+
+```
+yum install devtoolset-9-gcc-c++-9.1.1-2.6.el7.x86_64 centos-release-scl -y
+```
+
+The RHEL Chapel build instructions are the same for all distros with the exception of older distros such as CentOS 7; for these, the newer gcc compiler must first be enabled:
+
+```
+source /opt/rh/devtoolset-9/enable
+```
+
+The remaining RHEL Chapel download and build instructions follow those detailed above for Ubuntu Linux.
+
+<a id="l-python"></a> 
+### Python Environment - Anaconda (Linux)<sup><sup><sub><a href="#toc">toc</a></sub></sup></sup>
 As is the case with the MacOS install, it is highly recommended to [install Anaconda](https://docs.anaconda.com/anaconda/install/linux/) to provide a Python environment and manage Python dependencies:
 
 ```bash

README.md

@@ -115,6 +115,7 @@ For detailed prerequisite information and installation guides, please review [IN
 
 **Requirements List**
 * chapel 1.25.1
+* cmake >= 3.11.0
 * zeromq version >= 4.2.5, tested with 4.2.5 and 4.3.1
 * hdf5 
 * python 3.7 or greater
@@ -145,7 +146,23 @@ $(eval $(call add-path,/home/user/anaconda3/envs/arkouda))
 
 The `chpl` compiler will be executed with `-I`, `-L` and an `-rpath` to each path.
 
+The minimum cmake version is 3.11.0, which is not supported in older RHEL versions such as CentOS 7; in these cases, cmake must be downloaded, installed, and linked as follows. Note: while any version of cmake >= 3.11.0 should work, we tested exclusively with 3.11.0:
+
 ```
+# Export version number of cmake binary to be installed
+export CM_VERSION=3.11.0
+
+# Download cmake
+wget https://github.com/Kitware/CMake/releases/download/v$CM_VERSION/cmake-$CM_VERSION-Linux-x86_64.sh
+
+# Install cmake
+sh /opt/cmake-$CM_VERSION-Linux-x86_64.sh --skip-license --include-subdir
+
+# Link cmake version
+
+export PATH=./cmake-$CM_VERSION-Linux-x86_64/bin:$PATH
+```
+
 # If zmq and hdf5 have not been installed previously, execute make install-deps
 make install-deps