Include Google Colab installation script

pygmtsar/MANIFEST.in

@@ -1 +1,2 @@
 include pygmtsar/data/geoid_egm96_icgem.grd
+include pygmtsar/data/google_colab.sh

pygmtsar/pygmtsar/data/google_colab.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+
+# Install GMTSAR if needed
+count=$(ls /usr/local | grep -c GMTSAR)
+if [ "$count" -eq 0 ]; then
+    export DEBIAN_FRONTEND=noninteractive
+    apt-get update > /dev/null
+    apt install -y csh autoconf gfortran \
+        libtiff5-dev libhdf5-dev liblapack-dev libgmt-dev gmt > /dev/null
+    # GMTSAR codes are not so good to be compiled by modern GCC
+    apt install gcc-9 > /dev/null
+    update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 10
+    update-alternatives --config gcc
+    gcc --version | head -n 1
+    git config --global advice.detachedHead false
+    cd /usr/local && git clone -q --branch master https://github.com/gmtsar/gmtsar GMTSAR
+    # revert recent broken commit
+    cd /usr/local/GMTSAR && git checkout e98ebc0f4164939a4780b1534bac186924d7c998 > /dev/null
+    cd /usr/local/GMTSAR && autoconf > /dev/null
+    cd /usr/local/GMTSAR && ./configure --with-orbits-dir=/tmp > /dev/null
+    cd /usr/local/GMTSAR && make 1>/dev/null 2>/dev/null
+    cd /usr/local/GMTSAR && make install >/dev/null
+    # test one GMTSAR binary
+    /usr/local/GMTSAR/bin/make_s1a_tops 2>&1 | head -n 2
+fi
+
+# Install virtual framebuffer for interactive 3D visualization
+apt install -y xvfb > /dev/null
+pip3 install -q pyvista xvfbwrapper jupyter_bokeh
+# note: jupyter_bokeh for panel interactive visualization backend blocks tqdm progressbar