Update windows.md (#400)

Lot of folks encounter the python launcher error described in https://stackoverflow.com/questions/24627525/fatal-error-in-launcher-unable-to-create-process-using-c-program-files-x86. It is better to provide an alternate installation path that will not encounter that error.

Author: suresh-kandoth

doc/installation/windows.md

@@ -13,6 +13,10 @@ Once Python is installed and in the PATH environment variable, open a command pr
 ```shell
 C:\> pip install mssql-cli
 ```
+or use the following command if you encounter a launcher error
+```shell
+C:\> python -m pip install mssql-cli
+```
 
 ## Installation with daily preview build
 Daily preview builds are dropped in our storage account. To install the latest available version of mssql-cli, use the below command: