devtools: add a script to fetch and postprocess translations

Run this script from the root of the repository to update all translations from transifex.
It will do the following automatically:

- create a transifex configuration file
- fetch all translations
- post-process them into valid and committable format

contrib/devtools/README.md

@@ -69,3 +69,15 @@ If there are 'unsupported' symbols, the return value will be 1 a list like this
     .../64/test_bitcoin: symbol std::out_of_range::~out_of_range() from unsupported version GLIBCXX_3.4.15
     .../64/test_bitcoin: symbol _ZNSt8__detail15_List_nod from unsupported version GLIBCXX_3.4.15
 
+update-translations.py
+=======================
+
+Run this script from the root of the repository to update all translations from transifex.
+It will do the following automatically:
+
+- fetch all translations
+- post-process them into valid and committable format
+- add missing translations to the build system (TODO)
+
+See doc/translation-process.md for more information.
+