Windows has the command more. E.g. (Taken from Wikipedia)

To display the file named letter.txt on the screen, the user can type either of the following two commands:

 more < letter.txt
 type letter.txt | more 

So in your case you want hg log | more.

For heavier usage you will want something like UnxUtils or GnuWin32, which have a more powerful less utility.

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On Windows 10, you can install the Windows Subsystem for Linux:

The Windows Subsystem for Linux lets developers run Linux environments -- including most command-line tools, utilities, and applications -- directly on Windows, unmodified, without the overhead of a virtual machine.

Once installed, start bash.exe and run less /mnt/c/temp/test.txt to open the file test.txt located in c:\temp.

If you don't mind installing additional software gow is a nice toolkit with a set of standalone unix style tools that you can use, including less and more - it requires an install since it adds itself to path, but you can copy and use the install directory elsewhere as well.

Up-to-date less build for Windows is here:

Here you can find up-to-date less builds for Windows:

This are the reccomended Windows builds on the less official download page.

I install a ready-to-run less via choco:

choco install less

It uses the binary generated by the aforementioned less-Windows