Added SPFx (SharePoint Framework) gitignore

SPFx.gitignore

+#SharePoint Framework (SPFx)
+# Logs
+logs
+*.log
+npm-debug.log*
+
+# Dependency directories
+node_modules
+
+# Build generated files
+dist
+lib
+solution
+temp
+*.sppkg
+
+# Coverage directory used by tools like istanbul
+coverage
+
+# OSX
+.DS_Store
+
+# Visual Studio files
+.ntvs_analysis.dat
+.vs
+bin
+obj
+
+# Resx Generated Code
+*.resx.ts
+
+# Styles Generated Code
+*.scss.ts
\ No newline at end of file