Fix #114 add new installation instruction to the readme

The following additions were made to improve novice user installation experience in the cFS README.md

Added a brief introductory statement describing cFS to the top of the page
Added prerequisite software (make, cmake, gcc, and git) instruction to the Setup section
Added a statement specifying a possible third dependency for the GroundSystem (libcanberra-gtk-module) under the Send commands receive telemetry section
Reworded the redirection to the Guide-GroundSystem.md for questions regarding setup and installation

Additionally, some typos were corrected.

Resolves #114

README.md

@@ -95,7 +95,7 @@ Note: The steps above are for a debug, permissive mode build and includes deprec
 
 ## Send commands, receive telemetry
 
-The cFS-GroundSystem tool can be used to send commands and receive telemetry.  For details on using and setting up the Ground System, see the [Guide-GroundSystem.txt](https://github.com/nasa/cFS-GroundSystem/tree/master/Guide-GroundSystem.txt).  Note it depends on PyQt5 and PyZMQ:
+The cFS-GroundSystem tool can be used to send commands and receive telemetry.  For details on using and setting up the Ground System, see the [Guide-GroundSystem](https://github.com/nasa/cFS-GroundSystem/blob/main/Guide-GroundSystem.md).  Note it depends on PyQt5 and PyZMQ:
 
 1. Install PyQt5 and PyZMQ on your system.  Some systems may also require installing libcanberra-gtk-module.