Added Sentiment Analysis section for Russian language. The latter inc…

…ludes sentiment attitude extraction task description and reference to RuSentRel leaderboard. (sebastianruder#587)

README.md

@@ -75,6 +75,7 @@ For more tasks, datasets and results in Chinese, check out the [Chinese NLP](htt
 ### Russian
 
 - [Question answering](russian/question_answering.md)
+- [Sentiment Analysis](russian/sentiment-analysis.md)
 - [Summarization](russian/summarization.md)
 
 ### Spanish

russian/sentiment-analysis.md

@@ -0,0 +1,24 @@
+# Sentiment Analysis
+
+Sentiment analysis is the task of classifying the polarity of a given text.
+
+## RuSentRel
+
+The [RuSentRel](https://github.com/nicolay-r/RuSentRel) dataset
+consisted of analytical articles from Internet-portal inosmi.ru. These are translated into Russian texts in the domain of international politics obtained from foreign authoritative sources.
+The collected articles contain both the author's opinion on the subject matter of the article and a large number of references mentioned between the participants of the described situations. 
+The dataset contains 73 large analytical texts, labeled with about 2000 relations.
+
+**Sentiment Attitude Extraction task:** Given a subset of documents, in which every document includes: (1) text, (2) a list of mentioned named entities. 
+For each document it is required to complete a list of labeled entity pairs [(s<sub>1</sub>->o<sub>1</sub>, l<sub>1</sub>), ... (s<sub>n</sub>->o<sub>n</sub>, l<sub>n</sub>)], 
+for which text conveys the presence of the sentiment relation expressed by the subject towards the object (s<sub>i</sub>->o<sub>i</sub>) with sentiment l<sub>i</sub> ∈ [neg, pos] (see the example below).
+
+Task paper: https://arxiv.org/pdf/1808.08932.pdf
+
+The public leaderboard is available at [github repository](https://github.com/nicolay-r/RuSentRel-Leaderboard)
+
+| Example                                                                                                                                                                                                                                                     |
+|:----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ... Meanwhile <ins>Moscow</ins> has repeatedly emphasized that its activity in the <ins>Baltic Sea</ins> is a response precisely to actions of **<ins>NATO</ins>** and the escalation of the hostile approach to **<ins>Russia</ins>** near its eastern borders ...
+| (NATO->Russia, neg), (Russia->NATO, neg)                                                                                                                                                                                                                    |
+