docs(sidenav): escape pipes in markdown table

[GeorgDangl]

replace pipe "|" in markdown tables for correct rendering in a table cell in GitHub

The table in the sidenav readme looks currently like this:

With the fix, it looks like this:

This seems to be an old but unresolved issue with how GitHub renders MarkDown files / tables.

[mmalerba]

Thanks for the fix!

[kara]

Note: We should probably move the info in the table into sidenav.md as well, since the README isn't pushed to the docs site.

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