Theme barbuk - add venv glyph and fix venv display in ssh mode (#1681)

* Add python venv glyph

* Fix venv display (tested for local and ssh prompt)

* Add documentation for python venv

themes/barbuk/README.md

@@ -29,6 +29,7 @@ BARBUK_GIT_BRANCH_ICON=''
 BARBUK_HG_CHAR='☿ '
 BARBUK_SVN_CHAR='⑆ '
 BARBUK_EXIT_CODE_ICON=' '
+BARBUK_PYTHON_VENV_CHAR=' '
 ```
 
 ### Customize glyphs
@@ -97,3 +98,9 @@ chmod 400 /etc/sudoers.d/keepenv
 ```bash
 user@hostname in  ~/bash-it on  master ✓ ❯
 ```
+
+### Python venv
+
+```bash
+  flask ~/test on  master ✓ ❯
+```