Add upload-sources.bash and README.md to tools/i18n

The upload-sources.bash script can be used to upload the messages.json
file when it gets updated directly to Crowdin.

Also, the blocked users list has been updated.

Change-Id: I8fe8fbc47e7b780198f31711bd1a464d175b4546
diff --git a/tools/i18n/bump-translations.bash b/tools/i18n/bump-translations.bash
index 85c4b39..181f3cb 100644
--- a/tools/i18n/bump-translations.bash
+++ b/tools/i18n/bump-translations.bash
@@ -1,4 +1,11 @@
 #!/bin/bash
+#
+# Downloads updated translations from Crowdin and creates a new commit with the
+# new updates.
+#
+# This commit should be uploaded afterwards for review with the |git review|
+# command (take a look to check everything went well before uploading it).
+
 emptyTranslationFile="{}"
 
 # Download new translations