don't ignore coverage doc

.gitignore

@@ -1,4 +1,4 @@
-node_modules/
-coverage/
-.nyc_output/
-nyc_output/
+/node_modules/
+/coverage/
+/.nyc_output/
+/nyc_output/

docs/coverage/index.md

@@ -0,0 +1,100 @@
+---
+layout: layout
+---
+
+# Coverage
+
+This module uses [nyc](http://npm.im/nyc) to track code coverage, even
+across subprocess boundaries.  It is included by default, and there's
+nothing you need to do but enable it.  Adding coverage *will* make
+your tests run slightly slower, but that's to be expected.
+
+Nyc in turn uses [istanbul](http://npm.im/istanbul) to do the actual
+coverage code transformation and reporting.
+
+To generate coverage information, run your tests with the `--cov`
+argument.
+
+If you use this a lot, you may want to add `coverage` and
+`.nyc_output` to your `.gitignore` and/or `.npmignore` files.
+
+## Maximal Coverage 💯
+
+As of version 7, node-tap lets you easily enforce 100% coverage of all
+lines, branches, functions, and statements with one easy flag, if
+that's your thing:
+
+```json
+{
+  "scripts": {
+    "test": "tap test/*.js --100"
+  }
+}
+```
+
+If you do this in an open source module, please [join the exclusive
+100 club](/100/).
+
+## Travis-CI and Coveralls.io Integration
+
+You can very easily take advantage of continuous test coverage reports
+by using [Travis-CI](https://travis-ci.org) and
+[Coveralls](https://coveralls.io).
+
+1. Enable Travis-CI by signing up, enabling tests on your repo, and
+   adding a `.travis.yml` file to your repo.  You can use [this
+   module's .travis.yml file as an
+   example](https://github.com/tapjs/node-tap/blob/master/.travis.yml)
+2. Enable Coveralls.io by signing up, and adding the
+   repo.  Note the repo API token.
+3. Back at Travis-CI, add a private environment variable.  The name of
+   the environment variable is `COVERALLS_REPO_TOKEN`, and the value
+   is the token you got from Coveralls.
+4. When that token is set in the environment variable, `tap` will
+   automatically generate coverage information and send it to the
+   appropriate place.
+
+## Uploading Coverage to Other Services
+
+There's no requirement that you use Coveralls!  Any coverage service
+that understands `lcov` can be used as well.
+
+For example, using [CodeCov](https://codecov.io), you can do the
+following:
+
+1. Add `codecov` as a devDependency in your project with this command:
+
+        npm install codecov --save-dev
+
+2. Add a `test` script that generates coverage information, and a
+   `posttest` that uploads it to codecov:
+
+        {
+          "scripts": {
+            "test": "tap test/*.js --coverage",
+            "posttest": "tap --coverage-report=lcov && codecov"
+          }
+        }
+
+## Local Coverage Reporting
+
+Printing out a coverage report can be done along with tests, or after
+any covered test run, using the `--coverage-report=<type>` argument.
+
+The most popular types are `text` and `html`, but any report style
+supported by istanbul is available, including:
+
+- clover
+- cobertura
+- html
+- json
+- json-summary
+- teamcity
+- text
+- text-lcov
+- text-summary
+
+To specify a report format, you can use `--coverage-report=<type>`.
+The default type is `text`, which produces a pretty text-only table on
+the terminal.  If you specify `--coverage-report=html`, then tap will
+attempt to open a web browser to view the report after the test run.