diff --git a/README.md b/README.md
index b06c851..70105ad 100644
--- a/README.md
+++ b/README.md
@@ -32,7 +32,7 @@ Generate stats from Opencaching data or GPX files.
 
 To compile it requires:
 
-*   C++20 compliler (e.g. GCC-9 or Clang-8).
+*   C++ compliler supporting C++17 and a minor subset of C++2a (e.g. GCC-9 or Clang-8).
 *   meson (at least 0.47.0) + ninja build system
 *   libcurl: https://curl.haxx.se/libcurl/
 *   JSON for Modern C++: https://github.com/nlohmann/json
@@ -45,8 +45,11 @@ run `meson build; cd build; ninja`. You might need to set `CXX` variable to poin
 
 ### Credits
 
-Maps of Poland `Poland.png` and `Poland_big.png` come from `https://pl.wikipedia.org/wiki/Plik:Poland_location_map.svg` and are licensed under CC-BY-SA and GNU FDL.
-Map of Poland `Poland_relief.png` comes from `https://commons.wikimedia.org/wiki/File:Relief_Map_of_Poland.svg` and is licensed under CC-BY-SA.
-Map of Europe `Europe.png` comes from `https://pl.wikipedia.org/wiki/Plik:Europe_location_map.svg` and is licensed under PD.
-Map of Voivodeships of Poland come from `https://commons.wikimedia.org/wiki/File:Podlaskie_Voivodeship_location_map.svg`, `https://commons.wikimedia.org/wiki/File:Pomeranian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Kuyavian-Pomeranian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Warmian-Masurian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Masovian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lesser_Poland_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Greater_Poland_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Opole_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lower_Silesian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Silesian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lublin_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Subcarpathian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:West_Pomeranian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:%C5%9Awi%C4%99tokrzyskie_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lubusz_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:%C5%81%C3%B3d%C5%BA_Voivodeship_location_map.svg`
+* Maps of Poland `Poland.png` and `Poland_big.png` come from `https://pl.wikipedia.org/wiki/Plik:Poland_location_map.svg` and are licensed under CC-BY-SA and GNU FDL.
+
+* Map of Poland `Poland_relief.png` comes from `https://commons.wikimedia.org/wiki/File:Relief_Map_of_Poland.svg` and is licensed under CC-BY-SA.
+
+* Map of Europe `Europe.png` comes from `https://pl.wikipedia.org/wiki/Plik:Europe_location_map.svg` and is licensed under PD.
+
+* Maps of Voivodeships of Poland come from `https://commons.wikimedia.org/wiki/File:Podlaskie_Voivodeship_location_map.svg`, `https://commons.wikimedia.org/wiki/File:Pomeranian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Kuyavian-Pomeranian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Warmian-Masurian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Masovian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lesser_Poland_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Greater_Poland_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Opole_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lower_Silesian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Silesian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lublin_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Subcarpathian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:West_Pomeranian_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:%C5%9Awi%C4%99tokrzyskie_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:Lubusz_Voivodeship_location_map.svg`, `https://pl.wikipedia.org/wiki/Plik:%C5%81%C3%B3d%C5%BA_Voivodeship_location_map.svg`
 and are licensed under CC-BY-SA.