Update README.md

README.md

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 A convenient API based on Corpus2 library for reading, writing, and processing
 textual corpora represented as CCL (XML) documents.
 
+###### Requirements
+python3.6, corpus2
+
+To install Corpus2 you have to add new source for APT:
+
+```bash
+wget -q -O - http://apt.clarin-pl.eu/KEY.gpg | apt-key add -
+echo 'deb https://apt.clarin-pl.eu/ /' > /etc/apt/sources.list.d/clarin.list
+
+apt-get update && apt-get install corpus2-python3.6
+```
+
 Install
 =======