City Park

You need a few icon files as well, then copy and paste the following into an xml file (CityPark.xml) in the Mods folder. Note that I added the basic cost of 10 gold and 5 mats, you can remove that if you don't want.

<ImprovementTypes>

    <ImprovementType InternalName="K_CityPark">
        <DisplayName>City Park</DisplayName>
        <Description>City parks increase the Prestige produced by the settlement by 1.</Description>
        <TileDesign>K_CityPark</TileDesign>
        <ConstructionTileDesign>K_CityPark_UC</ConstructionTileDesign>
        <DrawnIcon>Gfx/TacticalIcons/K_CityPark.png</DrawnIcon>
        <DrawnIconConstruction>Gfx/TacticalIcons/K_CityPark_UC.png</DrawnIconConstruction>
        <Thumbnail>K_CityPark_Thumb.png</Thumbnail>
        <AllowedPerCity>1</AllowedPerCity>
        <ReqCityLevel>4</ReqCityLevel>
        <LaborToBuild>10.0</LaborToBuild>
        <SupportedTerrainType>Land</SupportedTerrainType>
        <SupportedTerrainType>City</SupportedTerrainType>
        <RequiresCity>True</RequiresCity>

        <Medallions>
            <All>K_CityPark_Thumb.png</All>
            <Border_All>
            </Border_All>
        </Medallions>

        <Prereq>
            <Type>Tech</Type>
            <Attribute>Civics_Amarian</Attribute>
            <Value>0</Value>
        </Prereq>

        <Prereq>
            <Type>Allegiance</Type>
            <Attribute>Kingdom</Attribute>
        </Prereq>

        <GameModifier InternalName="Prestige1">
            <ModType>Resource</ModType>
            <Attribute>Prestige</Attribute>
            <Value>1.0</Value>
            <PerTurn>1</PerTurn>
        </GameModifier>

        <GameModifier>
            <ModType>ConstructionResourceCost</ModType>
            <Attribute>Gold</Attribute>
            <Value>-10</Value>
        </GameModifier>
        <GameModifier>
            <ModType>ConstructionResourceCost</ModType>
            <Attribute>Materials</Attribute>
            <Value>-5</Value>
        </GameModifier>

        <GameModifier>
            <ModType>Resource</ModType>
            <Attribute>Gold</Attribute>
            <Value>-1.0</Value>
            <PerTurn>1</PerTurn>
        </GameModifier>       

        <AIData AIPersonality="AI_General">
            <AITag>Prestige</AITag>
        </AIData>
    </ImprovementType>
</ImprovementTypes>

Untested, but should work. Enjoy.

The easiest way to learn and work with the XML is to just copy and paste, seriously. Take an existing improvement, copy and paste it, and just edit the parts that need to change. Start simple and see if you can do that while just changing the name. Your 'new' improvement will show up in game with the new name, but will otherwise be the same as the original. If you can manage that, the rest will be just as easy.