Updated Preferred Chain (markdown)

Preferred-Chain.md

@@ -16,6 +16,19 @@ If the ACME CA provides multiple cert chain, you can use `--preferred-chain` to
 acme.sh  --issue -d example.com .....  --test    --preferred-chain  "Fake LE Root X2"
 ```
 
+You can also use part of the name:
+
+```
+acme.sh  --issue -d example.com .....  --test    --preferred-chain  "X2"
+```
+
+It's also case-insensitive:
+
+```
+acme.sh  --issue -d example.com .....  --test    --preferred-chain  "x2"
+```
+
+
 2. For Letsencrypt.org Production server:
 
     There are 2 chains provided:
@@ -31,4 +44,16 @@ acme.sh  --issue -d example.com .....  --server letsencrypt   --preferred-chain
 ```
 
 
+You can also use part of the name:
+
+```
+acme.sh  --issue -d example.com .....  --server letsencrypt   --preferred-chain  "ISRG"
+```
+
+It's also case-insensitive:
+
+```
+acme.sh  --issue -d example.com .....  --server letsencrypt    --preferred-chain  "isrg"
+```
+