AA/attester: add README docs

Signed-off-by: Xynnn007 <[email protected]>

attestation-agent/attester/README.md

@@ -0,0 +1,26 @@
+# Attester Plugins
+
+This crate provides attester plugins for different platforms. An [attester](https://www.rfc-editor.org/rfc/rfc9334.html#section-7.2) plugin can provide the following abilities
+
+- Get remote attestation evidence.
+- Extend runtime measurement.
+- Check the initdata binding.
+
+## Evidence Getter Tool
+
+This crate provides a simple tool to detect the current platform type and get related quote due to given report data.
+
+Build the binary
+```shell
+git clone https://github.com/confidential-containers/guest-components.git
+cd guest-components/attestation-agent/attester
+
+cargo build --features=bin --bin evidence_getter --release
+```
+
+Get evidence
+```shell
+echo $EVIDENCE_STRING | ../../target/release/evidence_getter 
+```
+
+Here, `$EVIDENCE_STRING` is a string/bytes of up to 64 bytes.