[gimp-web/testing] README: update some dependency information.

[Jehan Pagès <jehanp src gnome org>]

commit 3c5edee4fbdd3b8ac3459748fa1c96423b7d9afc
Author: Jehan <jehan girinstud io>
Date:   Sun Sep 24 17:21:10 2017 +0200

    README: update some dependency information.
    
    Trying for the first time to build this website locally. The pygeoip lib
    is necessary to run the plugin `gimp_mirrors` otherwise I get:
    > ImportError: No module named pygeoip
    Furthermore Pelican 3.7 was failing to build the website with various
    errors and warnings. I assume our code use an older version (it builds
    fine with 3.6.3).

 README |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/README b/README
index f43dffb..fb31658 100644
--- a/README
+++ b/README
@@ -27,11 +27,16 @@ The tools to build and test the site are Python, Pelican, and a couple of module
     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`
 
 Further information in greater detail can be found in the Pelican documentation 
(http://docs.getpelican.com/en/stable/).