Update 'FCNC Fitter'

FCNC-Fitter.md

@@ -1 +1,19 @@
-FCNC fitter was written by .
+FCNC fitter was originally written by Christoph Langenbruch. Then, it was modified by David Gerick to fit the needs of the B+->K\*(KSpi+)mumu analysis. Later, Renata Kopecna modified it further to be slightly more versatile, not have either verbose or super verbose modes only and to compile much faster. 
+
+## Compilation
+Cmake
+
+## spdlog
+Spdlog is a fast logging library. It is made for C++ and consists only of headers. Spdlog is used in FCNCfitter now, as the previous version only used two levels of verbosity (verbose and super verbose) using basic prints.
+
+The github repository can be found at 
+[https://github.com/gabime/spdlog/wiki/1.-QuickStart](https://github.com/gabime/spdlog/wiki/1.-QuickStart)
+
+For simple instalation guide and tutorials, see
+[https://spdlog.docsforge.com/master/](https://spdlog.docsforge.com/master/)
+
+
+
+
+
+## File structure