docs: add a README (#18)

Author: miampf

README.md

@@ -0,0 +1,48 @@
+# Tag
+
+A simple program to organize plain text files with tags.
+
+## Installation
+
+### As a binary
+
+Simply head to the [releases](https://github.com/miampf/tag/releases) page and download the latest release for your system.
+
+### From source
+
+Simply clone the repository and run `cargo build --release` to build the project.
+
+## Usage
+
+To use tag you must add a taglist as the first line of your text files. A tagline looks like the following:
+
+```
+tags: [#tag1 #tag2]
+```
+
+The tags in the tagline start with a `#` followed by letters (some none-ASCII letters are also supported), numbers, `_` and `-`. This tagline **must** be the first line of your file and **must not** be larger than one line. You can find the tagline grammar under [tagline.pest](./tagline.pest).
+
+Once you've added taglines to your local files you can run `tag`. `tag` will search all subdirectories of a given directory and check if tagged files match your search query.
+
+The `tag` help message:
+
+```
+Usage: tag [OPTIONS] <QUERY> <PATH>
+
+Arguments:
+  <QUERY>  Search query for the tags
+  <PATH>   The path that will be searched
+
+Options:
+  -s, --silent   Only print the paths of matched files
+  -h, --help     Print help
+  -V, --version  Print version
+  ```
+
+A query contains operators and tags. Usable operators are `&` for the logical AND, `|` for the logical OR and `!` as a unary NOT. Furthermore, you can nest queries by using parantheses. A query could look like this:
+
+```
+#tag1 & #tag2 | (!#tag3 & #tag4)
+```
+
+This query would match all files that contain `#tag1` AND `#tag2` OR files that don't contain `#tag3` while also containing `#tag4`. You can find the query grammar under [query.pest](./query.pest).