Update readme with verify instructions (#20)

* Update readme doc with instructions to verify timestamped tag

* Rephrase GPG program config in readme

README.md

@@ -22,3 +22,78 @@ jobs:
         with:
           customTagMessage: "Put anything you want here or nothing at all."
 ```
+
+### Create a timestamped tag
+
+To create a timestamped tag, simply push a tag to your Github repository.
+
+```
+git push origin <TAG_NAME>
+```
+
+The Github action will automatically create a new tag named `<TAG_NAME>-ots`.
+
+
+### Verify the timestamped tag
+
+Install opentimestamps-client:
+
+```
+pip install opentimestamps-client
+```
+
+Add the following bash script to your home directory:
+
+```bash
+#!/bin/sh
+
+# Wrapper for the ots-git-gpg-wrapper
+#
+# Required because git's gpg.program option doesn't allow you to set command
+# line options; see the doc/git-integration.md
+
+ots-git-gpg-wrapper \
+    --gpg-program "`which gpg`" \
+    --bitcoin-node http://<BITCOIN_USER>:<BITCOIN_PASS>@<BITCOIN_HOST>:<BITCOIN_PORT>/ \
+    -- "$@"
+
+```
+
+Optionally include a tor socks5-proxy in your script:
+
+```bash
+    --socks5-proxy "<PROXY_HOST>:<PROXY_PORT>" \
+```
+
+Configure your git to use the new script as the GPG program:
+
+```
+git config --global gpg.program <path to ots-git-gpg-wrapper.sh>
+```
+
+Use the git tag command to check the timestamped tag:
+
+```
+git tag -v <TAG_NAME>-ots
+```
+
+
+### Example
+
+```
+(venv) yzernik@yzernik-MacBookPro:~/work/open-timestamps-github-action$ git tag -v v1.0.2-ots
+object c08887fc4bcef5fe43efe2511a1a91beda9ada5b
+type commit
+tag v1.0.2-ots
+tagger OpenTimestamps Github Action <[email protected]> 1633583868 +0000
+
+OpenTimestamps Github Action
+Github repository: yzernik/open-timestamps-github-action
+Github actor: yzernik
+Running my own action as dogfood!
+ots: Success! Bitcoin block 703912 attests existence as of 2021-10-06 PDT
+ots: Good timestamp
+gpg: Signature made Wed 06 Oct 2021 10:17:48 PM PDT
+gpg:                using RSA key 4508375EC1594D8A284EFB5FAFD08F9C86FAE9CB
+gpg: Can't check signature: No public key
+```