Updating readme to describe the new default branch

[Evmaus-MS]

Updating the documentation slightly (and testing PR build validation).

[michaelcfanning]

2. Load and compile src\BinSkim.sln

this step is for developing changes 'Load and compile blah to develop changes to contribute.'

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Refers to: README.md:8 in 34c1e87. [](commit_id = 34c1e87, deletion_comment = False)

[michaelcfanning]

3. Execute output in bld\bin\BinSkim.Driver for testing

This is wrong. S/be

'Run BuildAndTest.cmd from the enlistment root to validate all changes before proposing a pull request.'

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Refers to: README.md:9 in 34c1e87. [](commit_id = 34c1e87, deletion_comment = False)

[michaelcfanning]