[rtems-docs commit] README.txt: Add info on CentOS 7 Software Collections for Python 3

[Joel Sherrill]

Module:    rtems-docs
Branch:    master
Commit:    5d72d63ca157f00e58afe750e281beda3c0b11f0
Changeset: http://git.rtems.org/rtems-docs/commit/?id=5d72d63ca157f00e58afe750e281beda3c0b11f0

Author:    Joel Sherrill <joel at rtems.org>
Date:      Wed Nov  6 18:26:53 2019 -0600

README.txt: Add info on CentOS 7 Software Collections for Python 3

---

 README.txt | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/README.txt b/README.txt
index 1567be6..cdd44fd 100644
--- a/README.txt
+++ b/README.txt
@@ -181,11 +181,31 @@ Ditaa:
 
   # pkg install ditaa
 
-CentOS 6 and 7
-~~~~~~~~~~~~~~
+CentOS 7
+~~~~~~~~
 
 PDF Quality: production
 
+Python 3:
+
+By default, CentOS 7 has Python 2.x. Luckily they now have Software
+Collections which lets you install and use a "collection" of newer
+software. As root, 
+
+  # yum install centos-release-scl
+  # yum install rh-python36
+
+Then you can create your own virtual Python environment
+for use with the Sphinx toolchain.
+
+  $ cd ~
+  $ python -m venv rtemsdocs
+
+When you want to use the Sphinx toolchain.
+
+  $ scl enable rh-python36 bash
+  $ source ~/rtemsdocs/bin/activate
+
 Sphinx:
 
   $ pip install -U sphinx
@@ -212,6 +232,8 @@ PDF:
      NOTE: The year (2016) and host OS (i386-linux) will change to
            reflect 32 or 64 bit and OS name.
 
+  You will also likely need to install the aspell RPM.
+
 Single HTML:
 
 NOTE: npm appears to be part of the EPEL repository for RHEL and CentOS.