Update usage_guide.md (dbcli#225)

Added spacing around troubleshooting link

Author: rabryst

doc/usage_guide.md

@@ -16,7 +16,7 @@ mssql-cli provides the following key enhancements over sqlcmd in the Terminal en
 - Multi-line edit mode
 - Configuration file support
 
-If you encounter any issues, see the[troubleshooting](#troubleshooting_guide.md)section for known issues and workarounds.
+If you encounter any issues, see the [troubleshooting](#troubleshooting_guide.md) section for known issues and workarounds.
 
 
 ## Options