docs/images: add gifs and images for features

This includes images and gifs for:
- add import
- add tags to struct fields
- call hierarchy
- completion signature help
- extract variable
- find all references
- generate interface implementation
- generate unit tests
- go to definition
- find implementations
- outline
- peek definition
- rename
- toggle test file
- upgrade dependencies
- workspace symbols

Change-Id: I32394891ba1ecbeef87d0a5f4b11be969675c0a9
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/284272
Trust: Suzy Mueller <suzmue@golang.org>
Run-TryBot: Suzy Mueller <suzmue@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/docs/images/addimport.gif b/docs/images/addimport.gif
new file mode 100644
index 0000000..facb79c
--- /dev/null
+++ b/docs/images/addimport.gif
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diff --git a/docs/images/addtagstostructfields.gif b/docs/images/addtagstostructfields.gif
new file mode 100644
index 0000000..b8efb03
--- /dev/null
+++ b/docs/images/addtagstostructfields.gif
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diff --git a/docs/images/callhierarchy.gif b/docs/images/callhierarchy.gif
new file mode 100644
index 0000000..86a1cd2
--- /dev/null
+++ b/docs/images/callhierarchy.gif
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diff --git a/docs/images/completion-signature-help.gif b/docs/images/completion-signature-help.gif
new file mode 100644
index 0000000..f3b4b93
--- /dev/null
+++ b/docs/images/completion-signature-help.gif
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diff --git a/docs/images/extract-variable.gif b/docs/images/extract-variable.gif
new file mode 100644
index 0000000..189f8f9
--- /dev/null
+++ b/docs/images/extract-variable.gif
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diff --git a/docs/images/findallreferences.gif b/docs/images/findallreferences.gif
new file mode 100644
index 0000000..21def35
--- /dev/null
+++ b/docs/images/findallreferences.gif
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diff --git a/docs/images/generateinterfaceimplementation.gif b/docs/images/generateinterfaceimplementation.gif
new file mode 100644
index 0000000..e8e8dd1
--- /dev/null
+++ b/docs/images/generateinterfaceimplementation.gif
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diff --git a/docs/images/generateunittestsforfunction.gif b/docs/images/generateunittestsforfunction.gif
new file mode 100644
index 0000000..ba0a518
--- /dev/null
+++ b/docs/images/generateunittestsforfunction.gif
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diff --git a/docs/images/gotodefinition.gif b/docs/images/gotodefinition.gif
new file mode 100644
index 0000000..048b85f
--- /dev/null
+++ b/docs/images/gotodefinition.gif
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diff --git a/docs/images/implementations.gif b/docs/images/implementations.gif
new file mode 100644
index 0000000..ed4aa60
--- /dev/null
+++ b/docs/images/implementations.gif
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diff --git a/docs/images/outline.png b/docs/images/outline.png
new file mode 100644
index 0000000..feeb0fe
--- /dev/null
+++ b/docs/images/outline.png
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diff --git a/docs/images/peekdefinition.gif b/docs/images/peekdefinition.gif
new file mode 100644
index 0000000..8102247
--- /dev/null
+++ b/docs/images/peekdefinition.gif
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diff --git a/docs/images/rename.gif b/docs/images/rename.gif
new file mode 100644
index 0000000..eddbd0f
--- /dev/null
+++ b/docs/images/rename.gif
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diff --git a/docs/images/toggletestfile.gif b/docs/images/toggletestfile.gif
new file mode 100644
index 0000000..55cbd76
--- /dev/null
+++ b/docs/images/toggletestfile.gif
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diff --git a/docs/images/upgradedeps.png b/docs/images/upgradedeps.png
new file mode 100644
index 0000000..ce12067
--- /dev/null
+++ b/docs/images/upgradedeps.png
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diff --git a/docs/images/workspace-symbols.gif b/docs/images/workspace-symbols.gif
new file mode 100644
index 0000000..18995f9
--- /dev/null
+++ b/docs/images/workspace-symbols.gif
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