add temp fix in openbabel install procedure for broken 2Dgen

ippisite/docs/source/install.rst

@@ -21,6 +21,9 @@ Important note: for now official openbabel distributions are bugged, especially
     sudo apt install cmake
     git clone https://github.com/openbabel/openbabel.git
     cd openbabel
+    #use a PR fixing the 2D layout problem, until it gets fixed
+    git fetch origin pull/1902/head:pr1902
+    git checkout pr1902
     mkdir build
     cd build
     cmake .. -DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_BINDINGS=ON -DRUN_SWIG=ON