root dir default realpath

`dotnet build` generates `compiler-diagnostics.sarif` in current dir(realpath) same as `*.csproj`,

if this tool default root dir as pwd, it will be great.

now:

```
dotnet build
cq sarif compiler-diagnostics.sarif gl-code-quality-report.json $(realpath)/
```

expect:

```
dotnet build
cq sarif compiler-diagnostics.sarif gl-code-quality-report.json
```