echo: update documentation link

[nelsonfigueroa]

• 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.

[tldr-bot]

Hello! I've noticed something unusual when checking this PR:

• The page pages.de/common/echo.md is outdated, based on number of commands, compared to the English page.
• The page pages.fr/common/echo.md is outdated, based on number of commands, compared to the English page.
• The page pages.it/common/echo.md is outdated, based on number of commands, compared to the English page.
• The page pages.ja/common/echo.md is outdated, based on number of commands, compared to the English page.
• The page pages.ko/common/echo.md is outdated, based on number of commands, compared to the English page.
• The page pages.ru/common/echo.md is outdated, based on number of commands, compared to the English page.
• The page pages.sr/common/echo.md is outdated, based on number of commands, compared to the English page.
• The page pages.zh_TW/common/echo.md is outdated, based on number of commands, compared to the English page.

Is this intended? If so, just ignore this comment. Otherwise, please double-check the commits.