MAINT, FIX: explicitly install pylossless in RTD (#181)

Let's see if this works... Since #154, readthedocs fails because importlib.metadata.version fails on the readthe docs build.

ref: https://stackoverflow.com/questions/75922593/sphinx-readthedocs-and-package-version

.readthedocs.yaml

@@ -21,3 +21,5 @@ python:
       - requirements: requirements.txt
       - requirements: docs/requirements_doc.txt
       - requirements: requirements_testing.txt
+      # Make sure we install the package itself
+      - requirements: .