doc: Make File store/get integer methods clearer

Add an example on how to store signed integers on less than 64 bits,
using one bit for the signedness.

(cherry picked from commit cd25d184a5f547d7e7b6332a255908aa00f4ddc7)

doc/classes/File.xml

@@ -54,28 +54,28 @@
 			<return type="int">
 			</return>
 			<description>
-				Returns the next 16 bits from the file as an integer.
+				Returns the next 16 bits from the file as an integer. See [method store_16] for details on what values can be stored and retrieved this way.
 			</description>
 		</method>
 		<method name="get_32" qualifiers="const">
 			<return type="int">
 			</return>
 			<description>
-				Returns the next 32 bits from the file as an integer.
+				Returns the next 32 bits from the file as an integer. See [method store_32] for details on what values can be stored and retrieved this way.
 			</description>
 		</method>
 		<method name="get_64" qualifiers="const">
 			<return type="int">
 			</return>
 			<description>
-				Returns the next 64 bits from the file as an integer.
+				Returns the next 64 bits from the file as an integer. See [method store_64] for details on what values can be stored and retrieved this way.
 			</description>
 		</method>
 		<method name="get_8" qualifiers="const">
 			<return type="int">
 			</return>
 			<description>
-				Returns the next 8 bits from the file as an integer.
+				Returns the next 8 bits from the file as an integer. See [method store_8] for details on what values can be stored and retrieved this way.
 			</description>
 		</method>
 		<method name="get_as_text" qualifiers="const">
@@ -297,7 +297,26 @@
 			</argument>
 			<description>
 				Stores an integer as 16 bits in the file.
-				[b]Note:[/b] The [code]value[/code] should lie in the interval [code][0, 2^16 - 1][/code].
+				[b]Note:[/b] The [code]value[/code] should lie in the interval [code][0, 2^16 - 1][/code]. Any other value will overflow and wrap around.
+				To store a signed integer, use [method store_64] or store a signed integer from the interval [code][-2^15, 2^15 - 1][/code] (i.e. keeping one bit for the signedness) and compute its sign manually when reading. For example:
+				[codeblock]
+				const MAX_15B = 1 &lt;&lt; 15
+				const MAX_16B = 1 &lt;&lt; 16
+
+				func unsigned16_to_signed(unsigned):
+				    return (unsigned + MAX_15B) % MAX_16B - MAX_15B
+
+				func _ready():
+				    var f = File.new()
+				    f.open("user://file.dat", File.WRITE_READ)
+				    f.store_16(-42) # This wraps around and stores 65494 (2^16 - 42).
+				    f.store_16(121) # In bounds, will store 121.
+				    f.seek(0) # Go back to start to read the stored value.
+				    var read1 = f.get_16() # 65494
+				    var read2 = f.get_16() # 121
+				    var converted1 = unsigned16_to_signed(read1) # -42
+				    var converted2 = unsigned16_to_signed(read2) # 121
+				[/codeblock]
 			</description>
 		</method>
 		<method name="store_32">
@@ -307,7 +326,8 @@
 			</argument>
 			<description>
 				Stores an integer as 32 bits in the file.
-				[b]Note:[/b] The [code]value[/code] should lie in the interval [code][0, 2^32 - 1][/code].
+				[b]Note:[/b] The [code]value[/code] should lie in the interval [code][0, 2^32 - 1][/code]. Any other value will overflow and wrap around.
+				To store a signed integer, use [method store_64], or convert it manually (see [method store_16] for an example).
 			</description>
 		</method>
 		<method name="store_64">
@@ -327,7 +347,8 @@
 			</argument>
 			<description>
 				Stores an integer as 8 bits in the file.
-				[b]Note:[/b] The [code]value[/code] should lie in the interval [code][0, 255][/code].
+				[b]Note:[/b] The [code]value[/code] should lie in the interval [code][0, 255][/code]. Any other value will overflow and wrap around.
+				To store a signed integer, use [method store_64], or convert it manually (see [method store_16] for an example).
 			</description>
 		</method>
 		<method name="store_buffer">