sign: add signature verification docs

Co-authored-by: julienvincent <[email protected]>

Author: pylbrecht

docs/config.md

@@ -1027,6 +1027,20 @@ as follows:
 backends.ssh.allowed-signers = "/path/to/allowed-signers"
 ```
 
+## Commit Signature Verification
+
+By default signature verification and display is **disabled** as it incurs a
+performance cost when rendering medium to large change logs.
+
+If you want to verify and display commit signatures, you can use the
+provided template functions.
+
+FIXME(pylbrecht): add example for using CryptographicSignature type
+
+See [CryptographicSignature Type](./templates.md#cryptographicsignature-type)
+for available template methods.
+
+
 ## Git settings
 
 ### Default remotes for `jj git fetch` and `jj git push`

docs/templates.md

@@ -93,6 +93,7 @@ This type cannot be printed. The following methods are defined.
 * `parents() -> List<Commit>`
 * `author() -> Signature`
 * `committer() -> Signature`
+* `signature() -> Option<CryptographicSignature>`
 * `mine() -> Boolean`: Commits where the author's email matches the email of the current
   user.
 * `working_copies() -> String`: For multi-workspace repository, indicate
@@ -129,6 +130,16 @@ The following methods are defined.
 * `.short([len: Integer]) -> String`
 * `.shortest([min_len: Integer]) -> ShortestIdPrefix`: Shortest unique prefix.
 
+### CryptographicSignature type
+
+The following methods are defined.
+
+FIXME(pylbrecht): add descriptions to methods
+
+* `.verify() -> String`
+* `.key() -> String`
+* `.display() -> String`
+
 ### Email type
 
 The following methods are defined.