Added README with install instructions.

README.md

+# Miscellaneous things to process high throughput sequencing data.
+
+This Python package also installs a shell script depending on samtools:
+`sam2indexedbam.sh`
+
+## Installing
+
+Get the source using `git clone git@gitlab.pasteur.fr:bli/libhts.git`, `cd` into it and run `python3 -m pip install .`
+
+It might also work directly:
+
+    python3 -m pip install git+ssh://git@gitlab.pasteur.fr/bli/libhts.git
+