Merge pull request #4 from ashmrtn/readme

Add license and readme

LICENSE

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+MIT License
+
+Copyright (c) 2023 ashmrtn
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# AllowTags
+
+AllowTags is a golang linter that checks all tags on struct fields have keys
+matching one of the given set. Also does some validation of tag formatting.
+
+AllowTags provides more peace of mind when working with struct tags, especially
+since the golang compiler won't report misspellings.
+
+## Installing
+AllowTags is provided as a go module and can be installed by running
+`go install github.com/ashmrtn/allowtags@latest`
+
+## Running
+AllowTags uses a similar front-end to `go vet`. You can run AllowTags by
+executing `allowtags --allow-key key1 --allow-key key2 <packages>` after
+installation. You can pass multiple packages to AllowTags by using the
+`...` expression, just like you would with other tools. For example, to check
+your whole project with AllowTags just run `allowtags --allow-key key1 ./...`.
+
+### Flags
+AllowTags requires all tags that it allows be explicitly given. To specify
+multiple tag keys pass the `--allow-key` flag multiple times, each time with a
+different tag key.
+
+## Limitations
+AllowTags uses a different parsing method than govet and the golang standard
+library's tag parser. This means it may give different error messages compared
+to govet and the standard library when run on malformed tags. However, AllowTags
+is built to be fairly lenient when parsing tags and attempts to find key-value
+pairs where possible.
+
+The rules that AllowTags parses by are loosely derived from documentation in the
+golang standard library [reflect package](https://pkg.go.dev/reflect#StructTag)
+empirical testing of the standard library's behavior, and the idea of trying to
+find key-value pairs where possible even if the tag is not formatted as
+expected.