Docs: Create thresholds.md (#24265)

* Create thresholds.md

* Update docs/sources/panels/thresholds.md

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

* Update thresholds.md

* Update thresholds.md

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

docs/sources/panels/thresholds.md

+title = "Thresholds"
+type = "docs"
+[menu.docs]
+identifier = "thresholds"
+parent = "panels"
+weight = 300
++++
+
+# Thresholds
+
+Thresholds set the color of either the value text or the background depending on conditions that you define.
+
+You can define thresholds one of two ways:
+* **Absolute** thresholds are defined based on a number. For example, 80 on a scale of 1 to 150.
+* **Percentage** thresholds are defined relative to minimum and maximums. For example, 80 percent.
+
+You can apply thresholds to the following visualizations:
+* Stat
+* Gauge
+* Bar gauge
+* Table
+* Graph
+
+## Default thresholds
+
+On visualizations that support it, Grafana sets default threshold values of:
+* 80 = red
+* Base = green
+* Mode = Absolute
+
+The **Base** value represents minus infinity. It is generally the “good” color.
+
+## Add a threshold
+
+You can add as many thresholds to a panel as you want. Grafana automatically sorts thresholds from highest value to lowest.
+
+> **Note:** These instructions apply only to the Stat, Gauge, Bar gauge, and Table visualizations. 
+
+1. Navigate to the panel you want to add a threshold to.
+1. Click the **Field** tab.
+1. Click **Add threshold**. 
+1. Grafana adds a threshold with suggested numerical and color values.
+1. Accept the recommendations or edit the new threshold.
+   * **Edit color:** Click the color dot you wish to change and then select a new color.
+   * **Edit number:** Click the number you wish to change and then enter a new number.
+   * **Thresholds mode -** Click the mode to change it for all thresholds on this panel.
+1. Click **Save** to save the changes in the dashboard.
+
+## Add a threshold to a Graph panel
+
+In the Graph panel visualization, thresholds allow you to add arbitrary lines or sections to the graph to make it easier to see when the graph crosses a particular threshold.
+
+1. Navigate to the graph panel you want to add a threshold to.
+1. On the Panel tab, click **Thresholds**.
+1. Click **Add threshold**.
+1. Fill in as many fields as you want. Only the **T1** fields are required.
+   * **T1 -** Both values are required to display a threshold.
+     * **lt** or **gt** - Select **lt** for less than or **gt** for greater than to indicate what the threshold applies to.
+     * **Value -** Enter a threshold value. Grafana draws a threshold line along the Y-axis at that value.
+   * **Color -** Choose a condition that corresponds to a color, or define your own color.
+     * **custom -** You define the fill color and line color.
+     * **critical -** Fill and line color are red.
+     * **warning -** Fill and line color are yellow.
+     * **ok -** Fill and line color are green.
+   * **Fill -** Controls whether the threshold fill is displayed.
+   * **Line -** Controls whether the threshold line is displayed.
+   * **Y-Axis -** Choose **left** or **right**.
+1. Click **Save** to save the changes in the dashboard.
+
+## Delete a threshold
+
+1. Navigate to the panel you want to add a threshold to.
+1. Click the **Field** tab. (Or **Panel** tab for a graph panel.)
+1. Click the trash can icon next to the threshold you want to remove.
+1. Click **Save** to save the changes in the dashboard.