updated generic linux build instructions

[Former user]

dev please remove my previous 2 issues they have errors.

cd /where/i/keep/my/games/

# legally obtain a gog installer and extract it to caesaria-gog-data

innoextract  setup_caesar3_2.0.0.9.exe  -d caesaria-gog-data

# clone and build caesaria

git clone https://bitbucket.org/dalerank/caesaria.git
cd caesaria
cmake .
make -j4


# start the game you just built, using the gog c3 game data

./bin/caesaria.linux -c3gfx ../caesaria-gog-data/app -c3music ../caesaria-gog-data/app/wavs -c3video../caesaria-gog-data/app/smk