* Documentation for extensible events labs flag
* Fix git protocol usage
Prevents this:
```
+ git clone git://github.com/matrix-org/matrix-js-sdk.git matrix-js-sdk --branch develop --depth 1
Cloning into 'matrix-js-sdk'...
fatal: remote error:
The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
```