[ENHANCEMENT] Make search syntax reference link more accessible

**Is your feature request related to a problem? Please describe.**
As I do not use this everyday, the exact search syntax is not committed to memory.
But the only way I can seem to find the [search syntax](https://github.com/GoogleChrome/webstatus.dev/blob/main/antlr/FeatureSearch.md) reference link is to enter an _incorrect_ syntax, like:
https://webstatus.dev/?q=asdasd%2Casdass
So that I can get the link highlighted in this error message:

**Describe the solution you'd like**
This is extremely useful information for users!
Make the link more easily accessible.
Perhaps at the bottom of the left nav, with the Issue and About links?

**Describe alternatives you've considered**
- Entering incorrect formats, as referenced above.
- Tried going to [the About link](https://github.com/GoogleChrome/webstatus.dev/wiki/About-Web-Platform-Status) in the lower-left nav, but none of the links there link to it, including [the "wiki" link](https://github.com/GoogleChrome/webstatus.dev/wiki/) which is useless.

**Additional context**
I think that should do, but feel free to reach out if there are any questions.