doc: fix grammar and formatting in compressdev guide

[ upstream commit 4c9484373fcd0aa4a240fdb2e797269eb2f26b9b ]

Small improvements made to the compressdev programmer's guide.
This includes rephrasing some sentences, fixing grammar,
and aligning formatting.

Fixes: a584d3b ("doc: add compressdev library guide")
Fixes: f7095d4 ("doc: clarify data plane error handling in compressdev")

Signed-off-by: Ciara Power <ciara.power@intel.com>
Acked-by: Fan Zhang <roy.fan.zhang@intel.com>