Base: Update diff(1) man page to latest set of options

Describe how to use the two new context and unified format options in
the diff utility. Also change the example comparison of two files so
they contain more lines as that is much more interesting (and useful).

Base/usr/share/man/man1/diff.md

@@ -5,7 +5,7 @@ diff - compare files line by line
 ## Synopsis
 
 ```**sh
-$ diff [files...]
+$ diff [options...] [files...]
 ```
 
 ## Description
@@ -16,16 +16,39 @@ Compare `files` line by line.
 
 * `files`: files to compare ex: `file1 file2`
 
+## Options
+
+* `-u`, `-U <context>`, `--unified <context>`: Write diff in unified format with `<unified>` number of surrounding context lines (default 3).
+* `-c`, `-C <context>`, `--context <context>`: Write diff in context format with `<context>` number of surrounding context lines (default 3).
+
 ## Examples
 
+First we create two files to compare:
+
+```sh
+$ printf '1\n2\n3\n' > file1
+$ printf '1\nb\n3\n' > file2
+```
+
+Here's how to view differences between the two files in normal format:
+
 ```sh
-# View differences in two files
-$ echo 123 > file1
-$ echo 456 > file2
 $ diff file1 file2
-1c1
-< 123
+2c2
+< 2
 ---
-> 456
+> b
 ```
 
+Here's how to view differences between the two files in unified format:
+
+```sh
+$ diff -u file1 file2
+--- file1
++++ file2
+@@ -1,3 +1,3 @@
+ 1
+-2
++b
+ 3
+```