Update README.md

README.md

 # xtrace-cpp
 Barebones C++ implementation of X-Trace compatible with latest brown tracing framework + baggage version
 
-# Building
+# Build Instructions
+
+## Dependencies
+
+To build the project, libconfig++-dev needs to be installed. 
+To install the library, run the following command.
+
+```
+sudo apt-get install libconfig++-dev
+```
+
+## Building
 
 ```
 mkdir build