* [DOCS] Extend documentation on global variables configuration
* [DOCS] Synchronize meaning of @psalm-taint-source input with source code
* [DOCS] Add documentation for conditional @psalm-taint-escape
* [DOCS] Add documentation for @psalm-taint-unescape
The example as-is would currently not flag the following code:
```
public function foo() {
$foo = $bad_data;
\shell_exec($foo);
}
```
Switching it to `bad_data` made it work.
