gc: add page

[07CalC]

Please see issue: #2580

This PR adds gc command which helps ount nodes, edges, connected components, or clusters in Graphviz .dot files

• The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• The page(s) have at most 8 examples.
• The page description(s) have links to documentation or a homepage.
• The page(s) follow the content guidelines.
• The page(s) follow the style guide.
• The PR title conforms to the recommended templates.

[CLAassistant]

All committers have signed the CLA.

[tldr-bot]

The build for this PR failed with the following error(s) at commit
44b6fe800ff53cebe8e0d23c81ca9aae2de37457:

pages/common/gc.md:1: TLDR001 File should contain no leading whitespace

Please fix the error(s) and push again.

[kbdharun]

LGTM, thanks for your contribution.