pw_bloat: Expand docs
pw_bloat: Expand docs

This change fills in the how to use section in the bloat documentation.

Change-Id: Ib66c0bb8f47b35fd64f4c7cc87226f49a88e3f3c

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed