Add SSH username to Git over SSH documentation example

```

(testvenv) williams-air:testvenv williamedwards$ pip3 install 'foobar @ git+ssh://example.com/foobar'
    fatal: '/foobar' does not appear to be a git repository
    fatal: Could not read from remote repository.

(testvenv) williams-air:testvenv williamedwards$ pip3 install 'foobar @ git+ssh://[email protected]/foobar'
...
Successfully installed foobar-0.0
```

Author: WilliamDEdwards

docs/html/topics/vcs-support.md

@@ -18,7 +18,7 @@ The supported schemes are `git+file`, `git+https`, `git+ssh`, `git+http`,
 `git+git` and `git`. Here are some of the supported forms:
 
 ```none
-MyProject @ git+ssh://git.example.com/MyProject
+MyProject @ git+ssh://git@git.example.com/MyProject
 MyProject @ git+file:///home/user/projects/MyProject
 MyProject @ git+https://git.example.com/MyProject
 ```