Switch readme to Markdown

Still looks great as plain text, can be easily converted to same by the
CMake install/package process, and makes for a much nicer display
in-browser.

CMakeLists.txt

@@ -259,7 +259,7 @@ install(
 
 install(
   FILES
-  README.txt
+  README.md
   DESTINATION .
   RENAME ${PROJECT_NAME}.txt
 )

README.md

@@ -0,0 +1,58 @@
+
+  SickJumps 0.1.0
+  ===============
+
+  A speed ramping plugin for [Avisynth](http://www.avisynth.nl).
+
+  ### Requirements ###
+  1. Avisynth 2.6 or greater, or Avisynth+
+  2. Microsoft's Visual C++ 2015 Redistributable
+
+  [email protected]  
+  [@ItEndsWithTens](https://twitter.com/ItEndsWithTens)
+
+  ### Usage ###
+
+    SickJumps(clip c, int "first_frame", int "last_frame",
+              float "start_multiplier", float full_multiplier",
+              float "up_seconds", float "down_seconds",
+              string "script_variable", float "end_multiplier")
+
+  **c** clip
+  - The input clip. Can be any colorspace and audio format.
+
+  **first_frame** int, default 0
+  - The first frame of the ramp up to full speed.
+
+  **last_frame** int, default c frame count - 1
+  - The last frame of the ramp down to the ending speed.
+
+  **start_multiplier** float, default 1.0
+  - The speed multiplier to use before the ramp up.
+
+  **full_multiplier** float, default 2.0
+  - The speed multiplier to use between ramp up and ramp down.
+
+  **up_seconds** float, default c length / 4.0  
+  **down_seconds** float, default c length / 4.0
+  - The resulting duration, in seconds, of the ramp up and ramp down.
+
+  **script_variable** string
+  - Assigns a string, containing some debug info, to the specified variable  
+    name. Said string is colon-delimited, and takes the following form:
+
+    ```"frame:X:multiplier:Y:section:Z"```
+
+    Respectively, it provides the current input frame number, multiplier, and  
+    a simple label describing what section ("before", "ramp up", "full speed",  
+    "ramp down", or "after") the current output frame resides in.
+
+    The string is updated each frame, and is intended for use with Avisynth's  
+    runtime environment. Be sure to set ScriptClip's after_frame to true so  
+    the variable gets set properly.
+
+    See the source distribution for an example script that demonstrates one  
+    approach to parsing the string and using some of its information.  
+
+  **end_multiplier** float, default start_multiplier
+  - The speed multiplier to use after the ramp down.