OsmoGsmTester: Add missing dependency python-smpplib

Change-Id: I9a6ad33d41c8a90317d079ff0d1f9640c48a2353
diff --git a/doc/manuals/chapters/install.adoc b/doc/manuals/chapters/install.adoc
index 41c85e4..ae8412a 100644
--- a/doc/manuals/chapters/install.adoc
+++ b/doc/manuals/chapters/install.adoc
@@ -25,6 +25,7 @@
   ofono \
   python3-pip
 pip3 install pydbus
+pip3 install git+git://github.com/podshumok/python-smpplib.git
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 IMPORTANT: ofono may need to be installed from source to contain the most