Update README.md

Updated instructions for linux.
Merge pull request #149 from noway421/patch-1

Update README.md
Realy fixed spectator mouse now

I revived e481553 commit back, add invert support (`if (!cg_invertMouseY) y = y;`) and applied this to all spectator mode. 
Commented condition is unnecessary now. 

Now both spectator modes behaves exactly like in Ace of Spades.
Update Client.cpp

Reverted to Toumal code, but now it's applied to all spec modes.
Fix build err (#152)
Merge pull request #162 from 7histle/master

Fix build err (#152)
Update README.md

Added "Clone OpenSpades repository" to the "Installation" section
Changed error text format
Merge remote-tracking branch 'origin/master'
Fixing the problem in the last commit
Fixed #155
Quick workaround for #166 (disables SSE/SSE2 completely when their support aren’t enabled)
Fixed #153
Fixed #138 (set `cg_reduceSmoke` to 1)
Fixed #121 (changed block damage of 0.75 SMG)
Player cannot use tools soon after sprinting
Update README.md

SDL2 from truck instead of old version. Related to #133
Merge pull request #171 from noway421/patch-3

Update README.md
Merge remote-tracking branch 'origin/master'
Fixed serious bug that switching players in spectating mode might cause program to enter an infinite loop