add README for locales tools scripts

tools/README.md

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+**Those tools can be used to keep in sync our locale in the app between different language and with android translations**
+
+
+
+## Step 1: Find unused key locales in EN
+
+`tools/unusedLocalizedString.py` is iterating over all root keys in _locales/en/message.json and try to find them on the code with a regex. If it does not find it, it will print a line with False.
+Some key exceptions are hardcoded to not report false negative
+
+
+So just run:
+`tools/unusedLocalizedString.py |grep False`
+and double check by searching in the app if you can effectively remove those keys.
+
+
+## Step 2: Sync keys between each locales on desktop
+
+This step removes every key in all locales not found in the locale EN.
+So if for example, you have a key in `it` which is not present in `en`, it will be removed and the `it` file will be written without it.
+
+A summary for each language file is printed on the screen to let you know if anything was changed during the process
+
+`python3 tools/compareLocalizedStrings.py`
+
+
+## Step 3: Map translations from android to desktop
+
+This step matches translations from android to desktop. It needs to be run for each locale you want to update.
+
+
+`python3 tools/mapAndroidTranslationsToDesktop.py fr <path_to_android_root_project>`
+
+Under the hood, it uses a item from the EN desktop locale called `androidKey` to find the matching translation for each locale.
+
+Note that if a desktop key does not have an `androidKey` set, it will just be skipped
+The goal is to have an androidKey for each item, if possible. But for now apps are too different for that to make sense.