Documentation: Add less(1) man page, and link to it in others

Author: https://github.com/petelliott
Commit: https://github.com/SerenityOS/serenity/commit/9b40208e3bc
Pull-request: https://github.com/SerenityOS/serenity/pull/8486
Reviewed-by: https://github.com/MaxWipfli
Reviewed-by: https://github.com/alimpfard ✅

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

@@ -0,0 +1,78 @@
+## Name
+
+`less` - A full-featured terminal pager.
+
+## Synopsis
+
+```**sh
+$ cat file | less [-PXem]
+$ less [-PXem] [file]
+$ cat file | more
+$ more [file]
+```
+
+## Description
+
+`less` is a terminal pager that allows backwards movement. It is inspired by,
+but largely incompatible with
+[GNU less](http://www.greenwoodsoftware.com/less/index.html).
+
+## Options
+
+* `-P`, `--prompt`: Set the prompt format string. See [Prompts](#Prompts) for more details.
+* `-X`, `--no-init`: Don't switch to the xterm alternate buffer on startup.
+* `-e`, `--quit-at-eof`: Immediately exit less when the last line of the document is reached.
+* `-m`, `--emulate-more`: Apply `-Xe`, set the prompt to `--More--`, and disable
+  scrollback. This option is automatically applied when `less` is executed as `more`
+
+## Commands
+
+Commands may be preceded by a decimal number `N`. Currently, this feature
+does not exist, and no command use `N`.
+
+| Command | Description |
+|---------|-------------|
+| `q` | Exit less. |
+| `j` or `DOWNARROW` or `ENTER` | Go to the next line. |
+| `k` or `UPARROW` | Go to the previous line. |
+| `SPACE` | Go to the next page. |
+
+## Prompts
+
+`less` accepts a special prompt string with the `-P` option. prompts accept a
+variety of format specifiers so that they adapt to `less`'s state.
+
+A `%` followed by a letter will be replaced with the associated variable. If
+such a variable does not exist, or currently has no value, it will be replaced
+with a `?`.
+
+| Variable | Description |
+|----------|-------------|
+| `%f` | Replaced with the name of the current file |
+| `%l` | Replaced with the current line number |
+
+A `?` followed by a letter acts as an if expression on the associated
+condition. `:` then acts as the else, and `.` acts as the end token. for example
+if you wanted to print 'true' if you are at the end of the file and 'false'
+otherwise, your prompt would be `?etrue:false.`. These expressions are
+arbitrarily nestable. If a condition does not exist, then it will always
+evaluate it's false branch.
+
+| Condition | Description |
+|----------|-------------|
+| `?f` | True when reading from a file other than stdin. |
+| `?e` | True when at the end of a file. |
+
+A `\\` followed by any character will be replaced with the literal value of the
+character. For instance, `\\%l` would render as `%l`.
+
+All other characters are treated normally.
+
+#### examples
+
+`less`'s current default prompt: `'?f%f :.(line %l)?e (END):.'`
+
+## See Also
+
+* [more(1)](more.md) For a simpler pager that less implements.
+* [man(1)](man.md) For serenity's manual pager, that uses less.

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

@@ -50,3 +50,7 @@ $ man 2 mkdir
 
 `man` looks for man pages under `/usr/share/man`. For example,
 this man page should be located at `/usr/share/man/man1/man.md`.
+
+## See Also
+
+* [less(1)](less.md) For the terminal pager that `man` uses by default

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

@@ -11,11 +11,16 @@ $ more
 ## Description
 
 `more` reads data from standard input and prints it to standard output, screen by screen.
+`more` is a symlink for [`less(1)`](less.md), which has a more emulation mode.
 
 ## Examples
 
 ```sh
 # dmesg | more
 ...
---[ more ]--
+--More--
 ```
+
+## See Also
+
+* [less(1)](less.md) For the more advanced terminal pager that implements more.