pip install virtualenv doesn't give you a virtualenv function on stock Ubuntu 18.04

[Ed McDonagh]

Need to install via apt, so need to add to apt install line.

[Ed McDonagh]

Installing virtualenv via apt to ref #650. [skip ci] docs only.

→ <<cset e933d6f6bae3>>

[Ed McDonagh]

Correcting minus to emdash. Refs #650. [skip ci] docs only.

→ <<cset e9665ec435ff>>

[Ed McDonagh]

Rewording more clumsy English. Refs #650. [skip ci] docs only.

→ <<cset bb96dbad9a1c>>

[Ed McDonagh]

Added refs #648, #649, #650 to changes. [skip ci] docs only

→ <<cset 1d02eb994959>>

[Ed McDonagh]

Merged in issue648etcDocsFor081 (pull request #214)

Fixes #647, #648, #649, #650, #654

→ <<cset d1b822782c6c>>

[Ed McDonagh]

Merged in release-0.8.1b2 (pull request #216)

Release 0.8.1b2

Some fixes, lots of docs. Refs #647, #646, #647, #648, #649, #650, #651, #652, #653, #654, #656

→ <<cset d5db3ea11366>>