re #630 - Updates docs to reflect new scenerios for /updateassemblyinfo and /ensureassemblyinfo

Author: Philo

docs/usage/command-line.md

@@ -24,4 +24,34 @@ It will update the following assembly attributes:
 
 Note that contrary to when using the [MSBuild Task](msbuild-task.md) the attributes must already exist in the `AssemblyInfo.cs` or `AssemblyInfo.vb` files prior to calling GitVersion.
 
-By adding `/updateassemblyinfofilename` the name of AssemblyInfo file to update can be set.
+By adding `/updateassemblyinfo <filenames>` the name of AssemblyInfo file to update can be set.  This switch can accept multiple files with the path to the file specified relative to the working directory. 
+
+GitVersion can generate an assembly info source file for you if it does not already exist.  Use the `/ensureassemblyinfo` switch alongside `/updateassemblyinfo <filename>`, if the filename specified does not exist it will be generated based on a known template that adds:
+
+* `AssemblyVersion` will be set to the `AssemblySemVer` variable.
+* `AssemblyFileVersion` will be set to the `MajorMinorPatch` variable with a appended `.0`.
+* `AssemblyInformationalVersion` will be set to the `InformationalVersion` variable.
+
+This can be done for *.cs, *.vb and *.fs files. 
+
+When requesting that GitVersion generate an assembly info file you are limited to only specifying a single `<filename>` within the `/updateassemblyinfo` switch, this is to prevent the creation of mulitple assembly info files with the same assembly version attributes.  If this occurs your build will fail.
+
+### Example: When AssemblyInfo.cs does not exist
+`GitVersion.exe /updateassemblyinfo AssemblyInfo.cs /ensureassemblyinfo`
+
+A file is generated that contains version attributes (`AssemblyVersion`, `AssemblyFileVersion`, `AssemblyInformationalVersion`)
+
+### Example: When AssemblyInfo.cs already exists
+`GitVersion.exe /updateassemblyinfo AssemblyInfo.cs /ensureassemblyinfo`
+
+All known attributes (`AssemblyVersion`, `AssemblyFileVersion`, `AssemblyInformationalVersion`) will be updated
+
+### Example: When AssemblyInfo.cs and AssemblyVersionInfo.cs do not exist
+`GitVersion.exe /updateassemblyinfo AssemblyInfo.cs AssemblyVersionInfo.cs /ensureassemblyinfo`
+
+Will result in command line argument error
+
+### Example: When AssemblyInfo.cs and AssemblyVersionInfo.cs already exist
+`GitVersion.exe /updateassemblyinfo AssemblyInfo.cs AssemblyVersionInfo.cs`
+
+Will iterate through each file and update known attributes (`AssemblyVersion`, `AssemblyFileVersion`, `AssemblyInformationalVersion`).