README.md clarify keylength arg and ECC default

Reorder and reword small portions of the keylength documentation and
make the ECC cert default explicitly stated in part 2 to avoid
confusion.

Fixes #6590

README.md

@@ -208,6 +208,8 @@ The certs will be placed in `~/.acme.sh/example.com/`
 
 The certs will be renewed automatically every **60** days.
 
+The certs will default to ECC certificates.
+
 More examples: https://github.com/acmesh-official/acme.sh/wiki/How-to-issue-a-cert
 
 
@@ -359,36 +361,33 @@ Ok, it's done.
 
 **Please use dns api mode instead.**
 
-# 10. Issue ECC certificates
+# 10. Issue certificates of different key types and lengths (ECC or RSA)
+
+Just set the `keylength` to a valid, supported, value.
+
+Valid values for the `keylength` parameter are:
 
-Just set the `keylength` parameter with a prefix `ec-`.
+1. **ec-256 (prime256v1, "ECDSA P-256", which is the default key type)**
+2. **ec-384 (secp384r1,  "ECDSA P-384")**
+3. **ec-521 (secp521r1,  "ECDSA P-521", which is not supported by Let's Encrypt yet.)**
+4. **2048   (RSA2048)**
+5. **3072   (RSA3072)**
+6. **4096   (RSA4096)**
 
 For example:
 
-### Single domain ECC certificate
+### Single domain with ECDSA P-384 certificate
 
 ```bash
-acme.sh --issue -w /home/wwwroot/example.com -d example.com --keylength ec-256
+acme.sh --issue -w /home/wwwroot/example.com -d example.com --keylength ec-384
 ```
 
-### SAN multi domain ECC certificate
+### SAN multi domain with RSA4096 certificate
 
 ```bash
-acme.sh --issue -w /home/wwwroot/example.com -d example.com -d www.example.com --keylength ec-256
+acme.sh --issue -w /home/wwwroot/example.com -d example.com -d www.example.com --keylength 4096
 ```
 
-Please look at the `keylength` parameter above.
-
-Valid values are:
-
-1. **ec-256 (prime256v1, "ECDSA P-256", which is the default key type)**
-2. **ec-384 (secp384r1,  "ECDSA P-384")**
-3. **ec-521 (secp521r1,  "ECDSA P-521", which is not supported by Let's Encrypt yet.)**
-4. **2048   (RSA2048)**
-5. **3072   (RSA3072)**
-6. **4096   (RSA4096)**
-
-
 # 11. Issue Wildcard certificates
 
 It's simple, just give a wildcard domain as the `-d` parameter.