We should update s_string to spell check the important plain-text files in the root of the WT source tree:

• CONTRIBUTING.rst

• INSTALL

• README

• RELEASE_INFO

This isn't quite as simple as adding these to the list of files that we run aspell on, since we currently use the --mode=ccpp option to aspell, which treats the input as C code and only checks what looks like comments and variable names.