Document use of Proxy for sOgrInfo

[yjacolin]

When network is behind a proxy, OGR failed. We can use environnement variable (GDAL_HTTP_PROXY) on the system level and then ogrinfo works. But it fails inside Talend.

We also setup:

• General proxy setup inside Talend DI
• Add a tSetEnv component
• Add a tSetProxy component

sOgrInfo component don't seem to use any of them.