Windows install instructions for documentation

[mpounsett]

Original report by Mayur Patil (Bitbucket: mayurp7, GitHub: mayurp7).

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Installation of nagiosplugin 1.2.4:
OS: Win 7 SP1 64 bits
Python: 2.7.x 32 bits and 3.5.x 64 bits
Installation mode: pip

For python 2.7, C:\Python27\python.exe
For python 3.5, C:\Python35\python3.exe

For nagiosplugin installation, Python 2.7

C:>python -m pip install nagiosplugin

For nagiosplugin installation, Python 3.5

C:>pip install nagiosplugin

[mpounsett]

Original comment by Christian Kauhaus (Bitbucket: ckauhaus, GitHub: ckauhaus).

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Thanks for the input, especially since I'm not a Windows user. I will update the README during the next release.