Add command line examples to the README.md

[jcouball]

Add these examples to the README.md:

semverify current # 0.1.0

semverify validate 1.0.0 # exitcode=0
semverify validate bad_version # exitcode=1

semverify patch # 0.1.0 -> 0.1.1
semverify minor # 0.1.1 -> 0.2.0
semverify major # 0.2.0 -> 1.0.0

# Pre-release with default pre-release type
semverify major --pre # 0.1.1 -> 1.0.0-pre.1

# Pre-release with non-default pre-release type
semverify major --pre --pre-type=alpha # 0.1.1 -> 2.0.0-alpha.1

# Increment pre-release
semverify pre # 1.0.0-alpha.1 -> 1.0.0-alpha.2

# Change the pre-release type
semverify pre --pre-type=beta # 1.0.0-alpha.2 -> 1.0.0-beta.1

# Create release from pre-release
semverify release # 1.0.0-beta.1 -> 1.0.0

[qlty-cloud-legacy]

Code Climate has analyzed commit 68318fb and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 100.0% (0.0% change).

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