add diff sizes' logos

assets/LICENSE.txt

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+This work is licensed under CC BY-SA 4.0. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/4.0/

assets/README.md

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+# the logo
+
+Some different sizes' logos are needed.
+
+## license
+
+<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-sa/4.0/88x31.png" /></a><br />This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.
+
+## the process of creation
+
+No professional designers are here. Thus the following steps involve many programer styles. :-)
+
+1. use excalidraw and export png and svg.
+
+    ```bash
+    # results
+    logo.excalidraw
+    logo.png
+    logo.svg
+    ```
+
+2. manually edit the `logo.svg` and make background transparent.
+
+    ```bash
+    # results
+    logo-transparent.svg
+    ```
+
+3. use python library [`svgutils`](https://github.com/btel/svg_utils) to make a strictly square figure. The [doc](https://svgutils.readthedocs.io/en/latest/tutorials/composing_multipanel_figures.html) is very useful.
+
+    ```python
+    from svgutils.compose import *
+    def get_standard_300x300(file_name):
+        fig = Figure(300, 300, 
+            Panel(
+                SVG(file_name),
+            ).move(-3, 12),
+        )
+        return fig
+
+    get_standard_300x300('logo-transparent.svg').save('300x300.svg')
+
+    # def get_other_size_from_standard(file_name, px):
+    #     fig = Figure(px, px, 
+    #         Panel(
+    #             SVG(file_name).scale(px/300.0),
+    #         ).move(-3*px/300.0, 12*px/300.0),
+    #     )
+    #     return fig
+
+    # get_other_size_from_standard('logo.svg',256).save('256x256.svg')
+    ```
+
+    ```bash
+    # results
+    300x300.svg
+    ```
+
+4. use `inkscape` command line to get different sizes' `.png` files.
+
+    ```bash
+    inkscape 300x300.svg -o 300x300.png
+
+    inkscape 300x300.svg -o 50x50.png -w 50 -h 50
+    
+    inkscape 300x300.svg -o 64x64.png -w 64 -h 64
+    inkscape 300x300.svg -o 256x256.png -w 256 -h 256
+    ```
+
+    ```bash
+    # results
+    50x50.png
+    64x64.png
+    256x256.png
+    ```