add git submodule

.gitmodules

@@ -0,0 +1,9 @@
+[submodule "public/dependence/pali-sentence"]
+	path = public/dependence/pali-sentence
+	url = https://github.com/iapt-platform/pali-sentence.git
+[submodule "public/dependence/word-statistics"]
+	path = public/dependence/word-statistics
+	url = https://github.com/iapt-platform/word-statistics.git
+[submodule "public/dependence/pali-similarity"]
+	path = public/dependence/pali-similarity
+	url = https://github.com/iapt-platform/pali-similarity.git