Make it more understandable

The original text could be quite confusing:

```
Open your ~/.ssh/config file, then modify the file, replacing ~/.ssh/id_ed25519 if you are not using the default location and name for your id_ed25519 key.

Host *
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/id_ed25519
```
1. It said "Open your ~/.ssh/config file, then modify the file, replacing ~/.ssh/id_ed25519" -- I was thinking, open that file, and then modify it, BUT HOW? AND THEN, replacing the file content of ~/.ssh/id_ed25519 ?  By what content?
2. And then it said, "if you are not using the default location and name for your id_ed25519 key"... location and name?  What location of name?  It turned out it meant the "path" and the "filename"... and "if you are using"? It actually meant "if you used" in the previous steps.

Author: KennethKinLum

content/github/authenticating-to-github/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent.md

@@ -91,7 +91,7 @@ Before adding a new SSH key to the ssh-agent to manage your keys, you should hav
       $ touch ~/.ssh/config
       ```
 
-    * Open your `~/.ssh/config` file, then modify the file, replacing ` ~/.ssh/id_ed25519` if you are not using the default location and name for your `id_ed25519` key.
+    * Open your `~/.ssh/config` file, then modify the file to the following lines. Replace the filename ` ~/.ssh/id_ed25519` below if you did not use the default location and filename for your `id_ed25519` key.
 
       ```
       Host *