Consume toolkit from npmjs (#16)

node_modules/@actions/tool-cache/README.md

@@ -4,4 +4,79 @@
 
 ## Usage
 
-See [src/tool-cache.ts](src/tool-cache.ts).
+#### Download
+
+You can use this to download tools (or other files) from a download URL:
+
+```
+const tc = require('@actions/tool-cache');
+
+const node12Path = await tc.downloadTool('http://nodejs.org/dist/v12.7.0/node-v12.7.0-linux-x64.tar.gz');
+```
+
+#### Extract
+
+These can then be extracted in platform specific ways:
+
+```
+const tc = require('@actions/tool-cache');
+
+if (process.platform === 'win32') {
+  tc.downloadTool('http://nodejs.org/dist/v12.7.0/node-v12.7.0-win-x64.zip');
+  const node12ExtractedFolder = await tc.extractZip(node12Path, 'path/to/extract/to');
+  
+  // Or alternately
+  tc.downloadTool('http://nodejs.org/dist/v12.7.0/node-v12.7.0-win-x64.7z');
+  const node12ExtractedFolder = await tc.extract7z(node12Path, 'path/to/extract/to');
+}
+else {
+  const node12Path = await tc.downloadTool('http://nodejs.org/dist/v12.7.0/node-v12.7.0-linux-x64.tar.gz');
+  const node12ExtractedFolder = await tc.extractTar(node12Path, 'path/to/extract/to');
+}
+```
+
+#### Cache
+
+Finally, you can cache these directories in our tool-cache. This is useful if you want to switch back and forth between versions of a tool, or save a tool between runs for private runners (private runners are still in development but are on the roadmap).
+
+You'll often want to add it to the path as part of this step:
+
+```
+const tc = require('@actions/tool-cache');
+const core = require('@actions/core');
+
+const node12Path = await tc.downloadTool('http://nodejs.org/dist/v12.7.0/node-v12.7.0-linux-x64.tar.gz');
+const node12ExtractedFolder = await tc.extractTar(node12Path, 'path/to/extract/to');
+
+const cachedPath = await tc.cacheDir(node12ExtractedFolder, 'node', '12.7.0');
+core.addPath(cachedPath);
+```
+
+You can also cache files for reuse.
+
+```
+const tc = require('@actions/tool-cache');
+
+tc.cacheFile('path/to/exe', 'destFileName.exe', 'myExeName', '1.1.0');
+```
+
+#### Find
+
+Finally, you can find directories and files you've previously cached:
+
+```
+const tc = require('@actions/tool-cache');
+const core = require('@actions/core');
+
+const nodeDirectory = tc.find('node', '12.x', 'x64');
+core.addPath(nodeDirectory);
+```
+
+You can even find all cached versions of a tool:
+
+```
+const tc = require('@actions/tool-cache');
+
+const allNodeVersions = tc.findAllVersions('node');
+console.log(`Versions of node available: ${allNodeVersions}`);
+```