Revert "Remove redundant installation instructions from README"

This reverts commit 21507985

README.md

 # ARQMath-eval
+
+### Install:
+
+```sh
+pip install git+https://gitlab.fi.muni.cz/xstefan3/arqmath-eval@master
+```
+
 ### Description
 
 This repository evaluates the performance of your information retrieval system