[feature] add hooks for using with pre-commit (#157)

.pre-commit-hooks.yaml

@@ -0,0 +1,7 @@
+-   id: deptry
+    name: deptry
+    description: deptry is a command line tool to check for issues with dependencies in a Python project, such as obsolete or missing dependencies.
+    entry: deptry .
+    language: system
+    always_run: true
+    pass_filenames: false

docs/docs/usage.md

@@ -130,4 +130,30 @@ An example of the contents of the resulting `deptry.json` file is as follows:
     "transitive": [],
     "misplaced_dev": []
 }
-```
+```
+
+## usage in pre-commit
+
+_deptry_ can be added to your [pre-commit](https://pre-commit.com/) rules.  Here is
+an example config for your .pre-commit-config.yaml file:
+
+```
+-   repo: https://github.com/fpgmaas/deptry.git
+    rev: <tag>
+    hooks:
+    - id: deptry
+      args:
+        - "--skip-missing"
+```
+
+Replace <tag> with one of the [tags](https://github.com/fpgmaas/deptry/tags) from the
+project or a specific commit.
+
+!!! note
+
+    This will only pull in the pre commit hooks config file from the version you have specified.  The
+    actual deptry that will be run will be the first one found in your path, so you will need
+    to add deptry to your local Python virtual environment.
+
+This requirement is due to deptry needing to be running within the same Python virtual environment
+whose dependencies it is analyzing.