add a quick and dirty readme

README.md

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+## related projects
+
+* [the original resynth gimp plugin in C++][orig]
+* [an updated gimp plugin in C and C++][gimp]
+* [syntex: similar algorithms based on resynth][syntex]
+
+[orig]: http://logarithmic.net/pfh/resynthesizer
+[gimp]: https://github.com/bootchk/resynthesizer/
+[syntex]: https://github.com/mxgmn/SynTex/
+
+## help
+
+```
+usage:
+  -a  --autism
+        sensitivity to outliers
+        range: (0,256);     default: 32
+  -N  --neighbors
+        points to use when sampling
+        range: (0,1024);    default: 29
+  -r  --radius
+        square neighborhood, always odd
+        range: (0,32);      default: [n/a]
+  -R  --circle-radius
+        circle neighborhood radius
+        range: (1,128);     default: [n/a]
+  -M  --tries
+        random points added to candidates
+        range: (0,65536);   default: 192
+  -p  --polish
+        extra iterations
+        range: (0,9);       default: 0
+  -m  --magic
+        magic constant, affects iterations
+        range: (0,255);     default: 192
+  -s  --scale
+        output size multiplier; negative values set width and height
+        range: (-8192,32);  default: 1
+  -S  --seed
+        initial RNG value
+        range: (0,);        default: 0 [time(0)]
+  {files...}
+        image files to open, resynthesize, and save as {filename}.resynth.png
+        required            default: [none]
+```
+
+apologies for the `radius`, `circle-radius`, and `polish` parameters.
+they should be properly described or removed.
+
+## notes
+
+includes header libraries from [nothings (stb)][stb] and [notwa (kyaa).][kyaa]
+
+[stb]: https://github.com/nothings/stb
+[kyaa]: https://gist.github.com/notwa/5d287d807ffe11bbb553462c9940445c#file-kyaa-md
+
+compile like
+```
+clang -std=gnu11 -lm -Ofast resynth.c -o resynth
+```
+
+extra flags that i use are
+```
+-Wall -Wextra -Werror=implicit-function-declaration -Winline -Wshadow
+-Wno-unused -Wno-padded -Wno-missing-field-initializers -Wno-misleading-indentation -Wno-disabled-macro-expansion -Wno-language-extension-token -Wno-unknown-warning-option
+```