Adds some instructions on How to update the changelogs

It's mostly nicked from /tg/'s wiki page, but has some other stuff, too.

html/changelogs/MagmaRam - changelog_instructions.yml

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+################################
+# Example Changelog File
+#
+# Note: This file, and files beginning with ".", and files that don't end in ".yml" will not be read. If you change this file, you will look really dumb.
+#
+# Your changelog will be merged with a master changelog. (New stuff added only, and only on the date entry for the day it was merged.)
+# When it is, any changes listed below will disappear.
+#
+# Valid Prefixes: 
+#   bugfix
+#   wip (For works in progress)
+#   tweak
+#   soundadd
+#   sounddel
+#   rscadd (general adding of nice things)
+#   rscdel (general deleting of nice things)
+#   imageadd
+#   imagedel
+#   maptweak
+#   spellcheck (typo fixes)
+#   experiment
+#################################
+
+# Your name.  
+author: MagmaRam
+
+# Optional: Remove this file after generating master changelog.  Useful for PR changelogs that won't get used again.
+delete-after: True
+
+# Any changes you've made.  See valid prefix list above.
+# INDENT WITH TWO SPACES.  NOT TABS.  SPACES.
+# SCREW THIS UP AND IT WON'T WORK.
+# Also, all entries are changed into a single [] after a master changelog generation. Just remove the brackets when you add new entries.
+# Please surround your changes in  double quotes ("), as certain characters otherwise screws up compiling. The quotes will not show up in the changelog.
+changes: 
+  - rscadd: "Added instructions on how to use the changelog updating scripts."

tools/GenerateChangelog/How to update the changelogs.txt

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+Taken mostly from https://tgstation13.org/wiki/Guide_to_Changelogs#Updating_the_Changelog with a few changes.
+
+First, install Python 2.7. Yes, it's outdated, but that's what the script is made to work with.
+Make sure that Python 2.7 and its Scripts/ folder is in PATH
+Upgrade pip, as outlined here https://pip.pypa.io/en/stable/installing/
+Once pip is installed, you will need to run two commands from your terminal or command prompt to install packages
+1. 'pip install PyYaml'
+2. 'pip install beautifulsoup4'
+
+Once all this is done, you should just be able to run ss13_genchangelog.py and sit back.
+
+If you get errors running it, two things are possible.
+1. You installed something wrong.
+2. Someone formatted their changelog wrong.
+Check where the error was, do a bit of troubleshooting, see if it wasn't #2. Fixing the syntax in the yaml files is pretty simple.