[gimp-web/migrate/py3] Update build instructions for py3 in README

[Pat David <patdavid src gnome org>]

commit 40f0836ae9d80564ee40630d9c9e7b980f95e6c1
Author: Pat David <patdavid gmail com>
Date:   Fri Apr 17 13:28:52 2020 -0500

    Update build instructions for py3 in README

 README.md | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)
---
diff --git a/README.md b/README.md
index 88c31a11..4eb84584 100644
--- a/README.md
+++ b/README.md
@@ -22,21 +22,13 @@ The tools to build and test the site are Python, Pelican, and a couple of module
 
 
 ### Getting the build environment
-1. Install Python 2.7.x.
-2. Install Pelican (`pip install pelican`).
-    Make sure that pip is using Python 2.7.x if you have multiple versions installed.
-    There may be a pip2.7 alias on your system.
-    You can also use a virtualenv to isolate the required Python environment.
-    Note: last I tested, Pelican 3.7.1 was failing to build the website.
-    Older Pelican 3.6.3 worked fine with our code: `pip2 install pelican==3.6.3`
-3. Install some extra components:
-    * For Markdown support (required):
-        `pip install Markdown`
-    * For fancy typography elements with typogrify:
-        `pip install typogrify`
-    * For geographical information from an IP address (optional for
-      plugin `gimp_mirrors`):
-        `pip install pygeoip`
+1. Install Python 3.x. (Tested and working on at least 3.5.7).  
+   For sanity, it is recommended to use a [virtual environment](https://docs.python.org/3/library/venv.html).
+    ```
+    python3 -m venv py3-venv
+    ```
+2. Install build requirements located in `py3-requirements.txt`.  
+   This can be done easily by running `pip install -r py3-requirements.txt`.
 
 Further information in greater detail can be found in the Pelican documentation 
(https://docs.getpelican.com/en/stable/).