Update README.md

Add section head

Author: prehensilecode

README.md

@@ -31,6 +31,7 @@ sudo singularity build alphafold.sif singularity/Singularity.def
 If your `/tmp` directory is small, you may need to set the [`SINGULARITY_TMPDIR`
 environment variable](https://sylabs.io/guides/3.3/user-guide/build_env.html#temporary-folders) to a directory on a filesystem with more free space.
 
+### Install and run
 To run, modify the `$ALPHAFOLD_SRC/singularity/run_singularity.py` and change the 
 section marked `USER CONFIGURATION`. At the least, you will need to modify the values
 of: