themes/sirup: Show VirtualEnv

[juanswan13]

Added the ability to show the current Virtual Env when using Python Virtual Env.
If there's not vitual env, the theme works normal.

[akinomyoga]

Thank you for your contribution.

Actually, this type of adjustment of themes depends on personal preferences, so I wouldn't merge it soon unless there is a strong reason that we need to merge it. Rather, we would recommend users customize it personally following the corresponding section in README.

Nevertheless, this PR can be used to demonstrate how to customize the theme, so let me add a label to this PR.

[akinomyoga]

I changed my mind and decided to merge this into master. The background is explained here.

• I added a commit 3cee730 and rebased.
• It seems there is already a segment of context information about ruby_gem, so it is more reasonable to put the python_venv information next to the ruby_gem information. I have moved the position of $python_venv to honor the original theme in commit 71d9a1b. I also made the style bold to make it match with ruby_gem.

If there are no further problems or suggestions, I'll wait for a few days and merge this. Thank you!

[akinomyoga]

Thanks, I have merged it.