Provide a sensible default for runestone_path

In the new monorepo the role of RUNESTONE_PATH is not as critical.  A default is fine.

Author: bnmnetp

.readthedocs.yaml

@@ -17,8 +17,7 @@ build:
             - poetry self add poetry-polylith-plugin
             - poetry self add poetry-multiproject-plugin
             - poetry install
-        post_build:
-            - RUNESTONE_PATH=.
+            # RUNESTONE_PATH is defined in the readthedocs control panel
 
 sphinx:
     configuration: docs/source/conf.py

components/rsptx/configuration/core.py

@@ -59,7 +59,8 @@ class Config:
     google_ga: str = ""
 
     # The path to the Runestone application inside web2py.
-    runestone_path: str = Path(os.environ.get("RUNESTONE_PATH")).resolve()
+
+    runestone_path: str = Path(os.environ.get("RUNESTONE_PATH", Path.home())).resolve()
 
     # _`book_path`: specify the directory to serve books from. For now, default to serving from the same place as the Runestone server, since the server uses some of these files.
     book_path: Path = runestone_path / "books"