Merge pull request #264 from Robbybp/fix-doc-typo

Correct docs for Windows build with custom branch

Author: ksbeattie

doc/build.md

@@ -131,7 +131,7 @@ To test the Windows build, run
 Note that the second argument to `build.ps1` is interpreted as an argument
 to `docker build`, so to run with a custom branch and no such argument, run
 ```powershell
-.\build.ps1 windows https://github.com/user/idaes-ext.git mybranch
+.\build.ps1 windows "" https://github.com/user/idaes-ext.git mybranch
 ```
 
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