Suggestion: add GitHub topic tags to repo

[mhucka]

Tiny and non-urgent suggestion: this repo's visibility might benefit from the addition of GitHub topic tags on the front page of the GitHub repo. (It currently has none.) Some possible tags as starting points:

• quantum computing
• quantum algorithms
• quantum circuit
• cirq
• simulation
• simulation-engine
• quantum circuit simulator

[mhucka]

I've added tags to the repo. Closing this as done.