Update README for Python 3.8 and newer

README.md

@@ -6,14 +6,13 @@ NilmDB requires Python 3.7 or newer.
 ## Prerequisites:
 
     # Runtime and build environments
-    sudo apt install python3.7 python3.7-dev python3.7-venv python3-pip
+    sudo apt install python3 python3-dev python3-venv python3-pip
 
-    # Optional: create a new Python virtual environment to isolate
-    # dependencies.  To leave the virtual environment, run "deactivate"
-    python -m venv venv
-    source venv/bin/activate
+    # Create a new Python virtual environment to isolate deps.
+    python3 -m venv ../venv
+    source ../venv/bin/activate   # run "deactivate" to leave
 
-    # Install all Python dependencies from PyPI.
+    # Install all Python dependencies
     pip3 install -r requirements.txt
 
 ## Test:
@@ -22,12 +21,12 @@ NilmDB requires Python 3.7 or newer.
 
 ## Install:
 
-Install it in a per-user location (e.g. `$HOME/.local/bin/nilmtool`)
+Install it into the virtual environment
 
-    python3 setup.py install --user
+    python3 setup.py install
 
-If you want to install it system-wide, you may need to also install the
-requirements system-wide:
+If you want to instead install it system-wide, you will also need to
+install the requirements system-wide:
 
     sudo pip3 install -r requirements.txt
     sudo python3 setup.py install